Edgar Filing: PRIMUS TELECOMMUNICATIONS GROUP INC

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As filed with the Securities and Exchange Commission on October 22, 2003

Registration No. 333-

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM S-3
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

PRIMUS TELECOMMUNICATIONS GROUP, INCORPORATED
(Exact name of registrant as specified in its charter)

Delaware
(State or other jurisdiction of incorporation or organization)

54-1708481
(I.R.S. Employer Identification No.)

1700 OLD MEADOW ROAD, SUITE 300
MCLEAN, VIRGINIA 22102
(703) 902-2800
(Address, including zip code, and telephone number, including area code of Registrant's principal executive offices)

K. PAUL SINGH
CHAIRMAN, PRESIDENT AND CHIEF EXECUTIVE OFFICER
PRIMUS TELECOMMUNICATIONS GROUP, INCORPORATED
1700 OLD MEADOW ROAD, SUITE 300
MCLEAN, VIRGINIA 22102
(703) 902-2800
(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

BRIAN J. LYNCH, ESQ.
COOLEY GODWARD LLP
ONE FREEDOM SQUARE
11951 FREEDOM DRIVE
RESTON, VIRGINIA 20190
TEL: (703) 456-8000

Approximate date of commencement of proposed sale to the public: As soon as practicable after this Registration Statement becomes effective.

If the only securities being registered on this form are being offered pursuant to dividend or interest reinvestment plans, please check the following box. o

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box. ý

If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

If this form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

If delivery of the prospectus is expected to be made pursuant to Rule 434, please check the following box. o

CALCULATION OF REGISTRATION FEE

Title Of Class Of Securities To Be Registered	Amount to be Registered	Proposed Maximum Offering Price Per Unit	Proposed Maximum Aggregate Offering Price	Amount of Registration Fee


3³/4% Convertible Senior Notes due September 15, 2010	$132,000,000	100%(1)	$132,000,000(1)	$10,678.80

Common Stock, par value $0.01 per share (2)	14,157,925(3)	—(4)	—(4)	—(4)

(1): Estimated solely for the purpose of calculating the registration fee pursuant to Rule 457(i) of the Securities Act of 1933, as amended.
(2): Each share of the registrant's common stock being registered hereunder, if issued prior to the termination by the registrant of its preferred share rights agreement, includes Series B Junior Participating Preferred Stock Purchase Rights pursuant to a rights agreement dated December 23, 1998, as amended, between the registrant and StockTrans, Inc., as Rights Agent. Prior to the occurrence of certain events, the Series B Junior Participating Preferred Stock Purchase Rights will not be exercisable or evidenced separately from the registrant's common stock and have no value except as reflected in the market price of the shares to which they are attached.
(3): Represents the number of shares of common stock that are initially issuable upon conversion of the 3³/4% Convertible Senior Notes due September 15, 2010 registered hereby. For purposes of estimating the number of shares of common stock to be registered hereunder, the registrant calculated the number of shares issuable upon conversion of the notes based on the initial conversion price of $9.3234 per share of common stock. In addition to the shares set forth in the table, pursuant to Rule 416 under the Securities Act the amount to be registered includes an indeterminate number of shares of common stock issuable upon conversion of the notes, as this amount may be adjusted as a result of stock splits, stock dividends and antidilution provisions.
(4): No additional consideration will be received for the common stock and, therefore, no registration fee is required pursuant to Rule 457(i).

THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS REGISTRATION STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(a) OF THE SECURITIES ACT OF 1933 OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID SECTION 8(a), MAY DETERMINE.

Subject To Completion, Dated October , 2003

The information in this prospectus is not complete and may be changed. The selling securityholders may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

PROSPECTUS

PRIMUS TELECOMMUNICATIONS GROUP, INCORPORATED

$132,000,000

3³/4% Convertible Senior Notes due September 15, 2010 and
Shares of Common Stock Issuable upon Conversion of the Notes

This prospectus covers resales by selling securityholders of our 3³/4% convertible senior notes due September 15, 2010 (the "notes") and shares of our common stock into which the notes are convertible.

The holders of the notes may convert the notes into shares of our common stock at any time at a conversion price of $9.3234 per share which is equivalent to a conversion rate of 107.257 shares per each $1,000 principal amount of notes, subject to adjustment in specified events.

We will pay interest on the notes on March 15 and September 15 of each year. The first interest payment will be made on March 15, 2004.

Upon the occurrence of a change of control, holders of the notes may require us to repurchase some or all of their notes for cash, common stock or a combination of cash and common stock.

The notes are our senior unsecured obligations and rank equally in right of payment with all of our existing and future senior debt and senior in right of payment to all of our existing and future subordinated debt. The notes are effectively subordinated to all of our existing and future secured debt to the extent of the value of the collateral securing such debt and structurally subordinated to all existing and future debt and other liabilities of our subsidiaries.

Prior to this offering, the notes have been eligible for trading on the PORTAL Market of the Nasdaq Stock Market. Notes sold by means of this prospectus are not expected to remain eligible for trading on the PORTAL Market. We do not intend to list the notes for trading on any national securities exchange or on the Nasdaq National Market.

Our common stock currently trades on the Nasdaq National Market under the symbol "PRTL." The last reported sale price on October 17, 2003 was $7.60 per share.

See "Risk Factors" beginning on page 6 of this prospectus to read about factors you should consider before buying the notes or our common stock.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is October , 2003

TABLE OF CONTENTS

		PAGE
SUMMARY		3
RISK FACTORS		6
USE OF PROCEEDS		20
DIVIDEND POLICY		20
SELECTED FINANCIAL DATA		21
DESCRIPTION OF THE NOTES		23
DESCRIPTION OF CAPITAL STOCK		38
MATERIAL UNITED STATES FEDERAL INCOME TAX CONSEQUENCES		47
SELLING SECURITY HOLDERS		53
PLAN OF DISTRIBUTION		55
WHERE YOU CAN FIND MORE INFORMATION		57
FORWARD-LOOKING INFORMATION		58
LEGAL MATTERS		60
EXPERTS		60

SUMMARY

This summary highlights some of the information in this prospectus. Because this is only a summary, it does not contain all of the information that may be important to you. To understand this prospectus, the notes, the common stock issuable upon conversion of the notes and our business, you should read the entire prospectus, particularly "Risk Factors" and the consolidated financial statements and related notes incorporated by reference into this prospectus.

PRIMUS

Primus Telecommunications Group, Incorporated and our subsidiaries (which, except as expressly noted otherwise, we refer to as "we" "us" or "Primus" in this prospectus), are a global, facilities-based telecommunications services provider offering international and domestic voice, Internet and data services to business and residential retail customers and other carriers located primarily in the United States, Australia, Canada, the United Kingdom and western Europe. Our focus is to service the demand for high quality, competitively priced international communications services that is being driven by the globalization of the world's economies, the worldwide trend toward telecommunications deregulation and the growth of Internet and data traffic.

We target customers with significant telecommunications needs, including small- and medium-sized enterprises, multinational corporations, residential customers, particularly ethnic customers, and other telecommunications carriers and resellers. We provide services over our global network, which consists of (1) 19 carrier-grade domestic and international gateway switching systems throughout North America, Australia, Europe and Japan; (2) approximately 250 points of presence within our principal service regions and other markets; (3) both owned and leased transmission capacity on undersea and land-based fiber optic cable systems; and (4) a global broadband asynchronous transfer mode (ATM) + Internet Protocol (IP) network and data centers.

We offer our customers a wide range of services, including:

•: international and domestic long distance services;
•: voice over Internet protocol (VoIP) services;
•: prepaid calling cards (including Virtual Mobile Network Services (VMNS)), toll-free services and reorigination services;
•: dial-up, dedicated and high-speed Internet access;
•: local services, primarily in Australia and Canada;
•: ATM+IP broadband services; and
•: managed and shared Web hosting services and applications.

We are a Delaware corporation with our principal executive offices located at 1700 Old Meadow Road, McLean, Virginia 22102. Our telephone number is (703) 902-2800 and our web site address is www.primustel.com. We make available free of charge through the "Investors" section of our web site our Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q, current reports on Form 8-K and all amendments to those reports as soon as reasonably practicable after such material is electronically filed with or furnished to the Securities and Exchange Commission. We include our web site address in this document only as an inactive textual reference and do not intend it to be an active link to our web site.

SECURITIES TO BE OFFERED

This prospectus relates to the offer and sale by the selling securityholders referenced in this prospectus of the following securities:

•: $132,000,000 convertible senior notes due September 15, 2010 and
•: shares of our common stock issuable upon conversion of the notes.

We issued and sold the notes in September 2003 to Lehman Brothers Inc., and Harris Nesbitt Corp., who are referred to in this prospectus as the initial purchasers, in transactions that were exempt from the registration requirements of the Securities Act of 1933. The initial purchasers believed that the persons to whom they resold the notes were "qualified institutional buyers," as defined in Rule 144A under the Securities Act.

The following is a summary of the material terms and considerations concerning the securities offered under this prospectus.

Issuer		Primus Telecommunications Group, Incorporated.
Securities Offered		$132.0 million aggregate principal amount of 3³/4% Convertible Senior Notes due 2010.
Maturity		September 15, 2010, unless earlier converted or repurchased, at your option, upon a change of control.
Interest Rate		3³/4% per year. Interest will be payable semi-annually on March 15 and September 15 of each year, commencing March 15, 2004. The initial interest payment will include accrued interest from September 15, 2003.
Conversion Rights		Holders may convert their notes into our common stock at any time prior to the close of business on the business day prior to the maturity date of the notes, unless previously repurchased, at a conversion price of $9.3234 per share (equal to a conversion rate of 107.257 shares per $1,000 principal amount of notes), subject to adjustment as described under "Description of the Notes —Conversion Rights."
Sinking Fund		None.
Change of Control Put Right		Upon a change of control of Primus, each holder may require us to repurchase all or a portion of the notes held by it at a repurchase price equal to 100% of the principal amount of the notes to be repurchased, plus accrued and unpaid interest thereon to, but excluding, the repurchase date. We may elect to pay the repurchase price with cash, our common stock or the common stock of the acquiring entity or its parent, or a combination of cash and common stock. If we pay the repurchase price in common stock, the common stock will be valued at 95% of the average closing sales price of the common stock on the Nasdaq National Market (or other national securities exchange on which the common stock is principally traded) for the five consecutive trading days ending on the third trading day prior to the repurchase date. See "Description of the Notes — Repurchase at Option of Holders Upon a Change of Control."

Events of Default		If there is an event of default on the notes, the principal amount of the notes, plus accrued and unpaid interest to the date of acceleration, may be declared immediately due and payable subject to certain conditions set forth in the indenture. These amounts automatically become due and payable in the case of certain types of bankruptcy or insolvency events of default involving Primus.
Ranking		The notes are our unsecured and unsubordinated obligations and rank equally in right of payment with all of our existing and future senior debt and rank senior in right of payment to all of our existing and future subordinated debt. In addition, the notes are effectively subordinated to all of our existing and future secured debt to the extent of the value of the collateral securing such debt, and structurally subordinated to all existing and future debt and other liabilities of our subsidiaries, including trade payables.
		The indenture governing the notes does not limit the amount of additional indebtedness that we can incur, assume or guarantee, nor does the indenture limit the amount of indebtedness and other liabilities that any subsidiary can incur, assume or guarantee. See "Risk Factors — Our high level of debt may adversely affect our financial and operating flexibility," "Risk Factors — Our high level of debt may adversely affect our ability to satisfy our obligations under the notes" and "Description of the Notes — Ranking."
Use of Proceeds		We will not receive any proceeds from the sale of the notes or the shares of common stock offered by this prospectus. See "Selling Securityholders."
Risk Factors		You should carefully consider the information set forth under "Risk Factors" in this document beginning on page 6 and all other information included or incorporated by reference in this document before deciding to purchase any notes.

RISK FACTORS

Any purchase of the notes or the shares of our common stock issuable upon conversion of the notes involves a high degree of risk. You should consider carefully the following information about these risks, together with the information under the caption "Forward-Looking Information" and the other information contained in or incorporated by reference to this prospectus before you decide to buy the notes. If any of the following risks actually materializes, our business, financial condition, results of operations and future growth prospects would likely be materially adversely affected. In these circumstances, the market price of the notes or our common stock would likely decline, and you may lose all or part of the money you paid to buy the notes.

Risks Related to Our Business

Our high level of debt may adversely affect our financial and operating flexibility.

We currently have substantial indebtedness and we and our subsidiaries may incur additional indebtedness in the future. As of June 30, 2003, our total consolidated indebtedness (including obligations under capital leases and equipment financings) was $542.0 million. The indenture governing the notes does not limit the incurrence of additional indebtedness. In addition, the terms of our other indebtedness limit, but do not prohibit, the incurrence of additional indebtedness.

The level of our indebtedness:

•: could make it difficult for us to make required payments of principal and interest on our outstanding debt, including the notes;
•: could limit our ability to obtain any necessary financing in the future for working capital, capital expenditures, debt service requirements or other purposes;
•: requires that a substantial portion of our cash flow, if any, be dedicated to the payment of principal and interest on our indebtedness and other obligations and, accordingly, such cash flow will not be available for use in our business;
•: could limit our flexibility in planning for, or reacting to, changes in our business;
•: results in us being more highly leveraged than many of our competitors, which may place us at a competitive disadvantage;
•: could discourage potential acquirors from making offers to acquire us; and
•: will make us more vulnerable in the event of a downturn in our business.

We have experienced historical, and may experience future, operating losses, negative free cash flow and net losses which may hinder our ability to meet our debt service or working capital requirements.

As of June 30, 2003, we had an accumulated deficit of $(708.6) million. We incurred net losses of $(63.6) million in 1998, $(112.7) million in 1999, $(174.7) million in 2000, $(306.2) million in 2001 and $(34.6) million in 2002.

Our recent net income and net revenue growth and recent positive free cash flow should not necessarily be considered to be indicative of future net income and net revenue growth or future free cash flow. We cannot assure you that our net income, net revenue or positive free cash flow will grow or be sustained in future periods. If we cannot sustain net income, operating profitability or positive free cash flow, we may not be able to meet our debt service or working capital requirements. These developments could have a material adverse impact on the trading prices of the notes and our common stock. See our discussion of free cash flow at note 2 to "Selected Financial Data."

Because a significant portion of our business is conducted outside the United States, fluctuations in foreign currency exchange rates could adversely affect our results of operations.

A significant portion of our net revenue is derived from sales and operations outside the United States. The reporting currency for our consolidated financial statements is the USD. The local currency of each country is the functional currency for each of our respective entities operating in that country. In the future, we expect to continue to derive a significant portion of our net revenue and incur a significant portion of our operating costs outside the United States, and changes in exchange rates have had and may continue to have a significant, and potentially adverse, effect on our results of operations. Our primary risk of loss regarding foreign currency exchange rate risk is caused by fluctuations in the following exchange rates: USD/Australian dollar (AUD), USD/Canadian dollar (CAD), USD/British pound (GBP), and USD/Euro dollar (EUR). In the six months ended June 30, 2003, the USD weakened compared to the AUD, CAD, GBP and EUR. As a result, our revenue of the subsidiaries whose local currency is the AUD, CAD and EUR increased 7%, 7% and 24% in local currency compared to the six months ended June 30, 2002, but increased 23%, 16% and 53% in USD, respectively. Our revenue of the subsidiaries whose local currency is the GBP decreased 13% in local currency from the six months ended June 30, 2002, but decreased 3% in USD. Due to the large percentage of our operations conducted outside of the United States, strengthening of the USD relative to one or more of the foregoing currencies could have an adverse impact on our future results of operations. We historically have not engaged in hedging transactions and do not currently contemplate engaging in hedging transactions to mitigate foreign exchange risks.

In addition, the operations of affiliates and subsidiaries in foreign countries have been funded with investments and other advances denominated in foreign currencies. Historically, such investments and advances have been long-term in nature, and we accounted for any adjustments resulting from currency translation as a charge or credit to "accumulated other comprehensive income (loss)" within the stockholders' deficit section of our consolidated balance sheets. In 2002, agreements with certain subsidiaries were put in place for repayment of a portion of the investments and advances made to the subsidiaries. As we anticipate repayment in the foreseeable future of these amounts, we recognize the unrealized gains and losses in foreign currency transaction gain (loss) on the consolidated statements of operations, and depending upon changes in future currency rates, such gains or losses could have a significant, and potentially adverse, effect on our results of operations.

Given our limited experience with, and the intense competition in, the Internet connectivity and data business, we may not be able to successfully operate or expand this part of our business.

Since 1999, we have been targeting businesses and residential customers for Internet and data services through the Primus brand and other businesses. We have been expanding and intend to continue to expand our offering of Internet, data and VoIP services worldwide. We anticipate offering a broad range of Internet protocol-based data and voice communications over our global broadband ATM+IP network. Currently, we provide Internet access services to business and residential customers in the United States, Australia, Canada, Japan, India, Brazil, and Spain, and offer Internet transmission services in the Indian Ocean/Southeast Asia regions through our earth stations in India.

Our experience with these services and these markets is limited. Furthermore, the market for dial-up and broadband Internet connectivity and related services is extremely competitive. Our primary competitors include incumbent operators, cable companies and other Internet service providers (ISPs) that have a significant national or international presence. Many of these operators have substantially greater resources, capital and operational experience than we do. We also expect we will experience increased competition from traditional telecommunications carriers and cable companies that expand into the market for Internet services. Therefore, our future operations involving these services may not generate operating or net income or positive free cash flow on a predictable basis and we may not be

able to successfully expand this part of our business. See our discussion of free cash flow at note 2 to "Selected Financial Data."

If we do not operate our network efficiently and generate additional traffic, we may not be able to achieve our operational growth goals.

Our long-term success depends on our ability to design, implement, operate, manage and maintain a reliable and cost-effective network. In addition, we rely on third parties to enable us to expand and manage our global network. If we fail to generate additional traffic on our network, if we experience technical or logistical impediments to our ability to migrate traffic onto our network, or if we experience difficulties with our third party providers, we may not achieve desired economies of scale or otherwise be successful in growing our business.

Our potential future growth may place a significant strain on our resources and, if not managed effectively, could result in operational inefficiencies and other difficulties.

Our continued growth and expansion may place a significant strain on our management, operational and financial resources, and increase demand on our systems and controls. We have expanded our retail operations through our recent acquisition of the small- and medium-sized enterprise (SME) voice customer base of Cable & Wireless (C&W) in the United States and the expansion of our VMNS product, particularly in Europe. To manage our growth effectively, we must continue to implement and improve our operational and financial systems and controls, purchase and utilize other transmission facilities, and expand, train and manage our employee base. If we inaccurately forecast the movement of traffic onto our network, we could have insufficient or excessive transmission facilities and disproportionate fixed expenses. As we proceed with our development, operational difficulties could arise from additional demand placed on our customer support, billing and management information systems, on our support, sales and marketing and administrative resources and on our network infrastructure. For instance, we may encounter delays or cost-overruns or suffer other adverse consequences in implementing new systems when required. In addition, our operating and financial control systems and infrastructure could be inadequate to ensure timely and accurate financial reporting.

The integration of our recent and future acquisitions ultimately may not provide the benefits originally anticipated by management and may distract the attention of our personnel from the operation of our business.

Acquisitions of businesses and customer lists, a key element of our historical growth strategy, involve operational risks, including the possibility that an acquisition does not ultimately provide the benefits originally anticipated by management. Moreover, there can be no assurance that we will be successful in:

•: identifying attractive acquisition candidates;
•: completing and financing additional acquisitions on favorable terms; or
•: integrating the acquired business or assets into our own.

There may be difficulty in integrating the service offerings, distribution channels and networks gained through acquisitions with our own. Successful integration of operations and technologies requires the dedication of management and other personnel, which may distract their attention from the day-to-day business, the development or acquisition of new technologies, and the pursuit of other business acquisition opportunities, and there can be no assurance that successful integration will occur in light of these factors.

We experience intense domestic and international competition which may adversely affect our ability to attract and retain customers and which can cause significant pricing pressures that adversely affect our net revenues per minute, results of operations and financial condition.

The long distance telecommunications and data industry is intensely competitive and is significantly influenced by the marketing and pricing decisions of the larger long distance industry and Internet access business participants. In addition, alternative services to traditional fixed wireline services, such as wireless and VoIP services, are a substantial competitive threat. The industry has relatively limited barriers to entry in the more deregulated countries with numerous entities competing for the same customers. Customers frequently change long distance providers and ISPs in response to the offering of lower rates or promotional incentives by competitors. Generally, customers can switch carriers at any time. Competition in all of our markets is likely to remain intense, or even increase in intensity and, as deregulatory influences are experienced in markets outside the United States, competition in non-United States markets is likely to become similar to the intense competition in the United States.

Our competitors in our core markets include, among others: AT&T, MCI, Sprint, the regional Bell operating companies (RBOCs) and the major wireless carriers in the United States; Telstra, SingTel Optus and Telecom New Zealand in Australia; Telus, BCE, CallNet and Allstream (formerly AT&T Canada) in Canada; and British Telecommunications plc. (BT), Cable & Wireless UK, AT&T, MCI, Colt Telecom, Energis and the major wireless carriers in the United Kingdom. Many of our competitors are significantly larger than we are and have:

•: substantially greater financial, technical and marketing resources;
•: larger networks;
•: a broader portfolio of service offerings;
•: greater control over transmission lines;
•: stronger name recognition and customer loyalty;
•: long-standing relationships with our target customers; and
•: lower leverage ratios.

As a result, our ability to attract and retain customers may be adversely affected.

Many of our competitors enjoy economies of scale that result in low cost structures for transmission and related costs that could cause significant pricing pressures within the industry. Several long distance carriers in the United States, including most recently, AT&T, MCI, Sprint, the RBOCs and the major wireless carriers, have introduced pricing and product bundling strategies that provide for fixed, low rates for calls within the United States. This strategy could have a material adverse effect on our net revenue per minute, results of operations and financial condition if increases in telecommunications usage and potential cost declines do not result in, or are insufficient to offset the effects of, such price decreases. Many companies emerging out of bankruptcy might benefit from a lower cost structure and might apply pricing pressure within the industry to gain market share. We compete on the basis of price, particularly with respect to our sales to other carriers, and also on the basis of customer service and our ability to provide a variety of telecommunications products and services. If such price pressures materialize, we may not be able to compete successfully in the future.

Furthermore, recent and pending deregulation in various countries may encourage new entrants to compete, including ISPs, cable television companies and utilities. For example, the United States and many other countries have committed to open their telecommunications markets to competition pursuant to an agreement under the World Trade Organization which began on January 1, 1998. Further, in the United States, as certain conditions have been met under the Telecommunications Act of 1996, the RBOCs have been allowed to enter the long distance market, AT&T, MCI and other long

distance carriers have been allowed to enter the local telephone services market, and any entity, including cable television companies and utilities, have been allowed to enter both the local service and long distance telecommunications markets.

A deterioration in our relationships with facilities-based carriers could have a material adverse effect upon our cost structure, service quality, network diversity, results of operations and financial condition.

We primarily connect our customers' telephone calls through transmission lines that we lease under a variety of arrangements with other facilities-based long distance carriers. Many of these carriers are, or may become, our competitors. Our ability to maintain and expand our business depends on our ability to maintain favorable relationships with the facilities-based carriers from which we lease transmission lines. If our relationship with one or more of these carriers were to deteriorate or terminate, it could have a material adverse effect upon our cost structure, service quality, network diversity, results of operations and financial condition. Moreover, we lease transmission lines from some vendors that currently are subject to tariff controls and other price constraints, which in the future may be changed.

Uncertainties and risks associated with international markets could adversely impact our international operations.

We have significant international operations. In many international markets, the incumbent carrier is likely to:

•: control access to, and pricing of, the local networks;
•: enjoy better brand recognition and brand and customer loyalty; and
•: have significant operational economies of scale, including a larger backbone network and more correspondent agreements.

Moreover, the incumbent carrier may take many months to allow competitors, including us, to interconnect to its switches within its territory. There can be no assurance that we will be able to:

•: obtain the permits and operating licenses required for us to operate;
•: obtain access to local transmission facilities on economically acceptable terms; or
•: market services in international markets.

In addition, operating in international markets generally involves additional risks, including:

•: unexpected changes in regulatory requirements, tariffs, customs, duties and other trade barriers;
•: difficulties in staffing and managing foreign operations;
•: problems in collecting accounts receivable;
•: political risks;
•: fluctuations in currency exchange rates;
•: restrictions associated with the repatriation of funds;
•: technology export and import restrictions; and
•: seasonal reductions in business activity.

Our ability to operate and grow our international operations successfully could be adversely impacted by these risks and uncertainties.

Rapid changes in the telecommunications industry could adversely affect our competitiveness and our financial results.

The telecommunications industry is changing rapidly due to:

•: deregulation;
•: privatization;
•: technological improvements;
•: availability of alternative services such as wireless and VoIP;
•: expansion of infrastructure; and
•: the globalization of the world's economies.

If we do not adjust our contemplated plan of development to meet changing market conditions, we may not be able to compete effectively. The telecommunications industry is marked by the introduction of new product and service offerings and technological improvements. Achieving successful financial results will depend on our ability to:

•: anticipate, assess and adapt to rapid technological changes; and
•: offer, on a timely and cost-effective basis, services that meet evolving industry standards.

If we do not anticipate, assess or adapt to such technological changes at a competitive price, maintain competitive services or obtain new technologies on a timely basis or on satisfactory terms our financial results may be materially and adversely affected.

Natural disasters could adversely affect our business by damaging our network facilities or curtailing voice or data traffic.

Many of the geographic areas where we conduct our business may be affected by natural disasters, including hurricanes and tropical storms. Hurricanes, tropical storms and other natural disasters could have a material adverse effect on our business by damaging our network facilities or curtailing voice or data traffic as a result of the effects of such events, such as destruction of homes and businesses.

Terrorist attacks and other acts of violence or war may affect the market on which our securities trade, the markets in which we operate, our operations and our profitability.

Terrorist attacks, such as the attacks that occurred in New York and Washington, D.C. on September 11, 2001, and other recent worldwide terrorist actions, may negatively affect our operations and your investment in Primus. We cannot assure you that there will not be further terrorist attacks that impact our employees, network facilities or support systems, either in the United States or in any of the other countries in which we operate. Certain losses resulting from these types of events are uninsurable and others are not likely to be covered by our insurance.

The United States has recently been engaged in an armed conflict with Iraq, and may enter into additional armed conflicts in the future. The consequences of any armed conflicts are unpredictable, and we may not be able to foresee events that could have an adverse effect on our business.

Terrorist attacks or armed conflicts may directly impact our business operations through damage or harm to our employees, network facilities or support systems, increased security costs or the general curtailment of voice or data traffic. Any of these events could result in increased volatility in or damage to Primus and the United States and worldwide financial markets and economies. They also could result in a continuation of the current economic uncertainty in the United States or abroad, which could have a material adverse effect on our operating results and financial condition.

The loss of our key personnel could materially and adversely affect our business and future prospects.

We depend upon the efforts of our management team and our key technical, marketing and sales personnel, particularly those of K. Paul Singh, our Chairman, President and Chief Executive Officer. If we lose the services of one or more of these key individuals, particularly Mr. Singh, our business and its future prospects could be materially and adversely affected. We have entered into an employment agreement with Mr. Singh, with an original term through May 30, 1999, but which has been renewed annually through May 30, 2004. We do not maintain any key person life insurance on the lives of any officer, director or key employee. Our future success will also depend on our ability to attract and retain additional key management and technical and sales personnel required in connection with the growth and development of our business. If we are not successful in attracting and retaining such executives and personnel, our business and future prospects could be materially and adversely affected.

We are subject to potential adverse effects of regulation which may have a material adverse impact on our competitive position, growth and financial performance.

Our operations are subject to constantly changing regulation. There can be no assurance that future regulatory changes will not have a material adverse effect on us, or that regulators or third parties will not raise material issues with regard to our compliance or noncompliance with applicable regulations, any of which could have a material adverse effect upon us.

As a multinational telecommunications company, we are subject to varying degrees of regulation in each of the jurisdictions in which we provide our services. Local laws and regulations, and the interpretation of such laws and regulations, differ significantly among the jurisdictions in which we operate. Future regulatory, judicial, legislative and government policy changes may have a material adverse effect on us and domestic or international regulators or third parties may raise material issues with regard to our compliance or noncompliance with applicable regulations, and therefore may have a material adverse impact on our competitive position, growth and financial performance.

In the United States, regulatory considerations that affect or limit our business include the following:

•: The need to comply with federal and state regulations. Through our operating subsidiaries, we are regulated at the federal level by the Federal Communications Commission (FCC) and at the state level by state public service commissions. We are required to maintain FCC authorizations for our international telecommunications services and state certifications and tariffs for our intrastate services. We are subject to various regulatory policies that affect the conditions under which we are permitted to operate, such as the common carrier requirements not to unreasonably discriminate among customers and to charge just and reasonable rates. We are also subject to certain foreign ownership limitations and the requirement to comply with various FCC and state reporting and fee obligations. Compliance with FCC and state regulations, challenges by third parties to our state tariffs, or complaints about our practices could cause us to incur substantial expenses. Further, the FCC and the state public service commissions have broad authority to sanction us or revoke our authorizations if we violate applicable law.
•: Difficulty in predicting change to government regulation, enforcement and interpretation of telecommunications laws. Our business may be harmed if we do not obtain or retain the necessary governmental approval for our services or if we fail to comply with applicable laws. Enforcement and interpretations of these laws and regulations can be unpredictable and are often subject to the informal views of government officials.
•: Changes in federal and state policies toward VoIP service. The future regulatory classification of VoIP telephony is difficult to predict. If federal and/or state regulators decide that VoIP is a

regulated telecommunications service, our VoIP services may be subject to burdensome regulatory requirements and fees and certain of our operating costs may increase.

•: Changes in access charges, universal service and regulatory fee payments. Changes in access charges, universal service and regulatory fee payments will affect our cost of providing long distance services and could materially adversely affect our business, financial condition, results of operations and prospects.

In Australia, regulatory considerations that affect or limit our business include the following:

•: The need to comply with federal regulations. We are regulated at the federal level by the Australian Communications Authority (ACA) for technical regulation and licensing and the Australian Competition and Consumer Commission (ACCC) for competition matters, including access and enforcement of competitive safeguards. The telecommunications industry is not regulated at the state level in Australia. We are required to maintain a carrier license if we own certain transmission facilities. We are subject to various regulatory policies that affect the conditions under which we are permitted to operate, such as customer service guarantee standards. We are potentially subject in our telecommunications license to conditions that apply to foreign ownership (although this does not currently apply) and the requirement to comply with various ACA and ACCC reporting and fee obligations. Compliance with regulations or complaints about our practices could cause us to incur substantial expenses. Further, the ACA and the ACCC have broad authority to sanction us or (in the case of the ACA) to cancel our license if we violate applicable law.
•: Difficulty in predicting change to government regulation, enforcement and interpretation of telecommunications laws. Our business may be harmed if we do not obtain or retain the necessary governmental approval for our services or if we fail to comply with applicable laws. Enforcement and interpretations of these laws and regulations can be unpredictable and are often subject to the informal views of government officials.
•: Changes in federal policies toward VoIP service. The future regulatory classification of VoIP telephony is difficult to predict. Currently we do not have peering arrangements with Tier 1 ISPs, such as Telstra, SingTel Optus, Telecom New Zealand and UUnet. We therefore pay fees for interconnection that are not paid by these Tier 1 ISPs. If federal regulators decide that VoIP should become a declared telecommunications service, our VoIP services may be subject to burdensome regulatory requirements and fees and certain of our operating costs may increase.
•: Changes in access charges, universal service and regulatory fee payments. Changes in access charges, universal service and regulatory fee payments will affect our cost of providing long distance services and could materially and adversely affect our business, financial condition, results of operations and prospects. We pay termination charges for calls from our network to mobile (cellular) telephone services. Carriers must meet the universal service obligation (USO) and the digital data service obligation to assist in providing all Australians, particularly those living in remote areas, with reasonable access to standard telephone services and digital data services. Telstra is currently the sole universal service provider. One of our subsidiaries, Hotkey Internet Services, has been approved as a special digital service provider. Since 2000, the responsible Minister of the Australian government may make a determination of the amount of USO subsidies, with advice from the Australian Communications Authority. No methodology is provided in any legislation and the Minister could make a determination of a universal service levy (USL) that would be material to us.

In Canada, regulatory considerations that affect or limit our business include the following:

•: The need to comply with federal regulations. Although we operate as a reseller and our rates and terms of service are therefore not subject to direct regulation by the Canadian Radio Television

and Telecommunications Commission (CRTC) pursuant to the Canadian Telecommunications Act, we are required to maintain a license for our international telecommunications services and registration as reseller of long distance services. We are subject to foreign ownership restrictions that affect the conditions under which we are permitted to operate (i.e., which prevent us from owning and operating transmission facilities or operating as a competitive local exchange carrier (CLEC)). We are also required to make contribution payments to support universal access. Compliance with CRTC regulations or complaints about our practices could cause us to incur substantial expenses. Further, the CRTC has authority to revoke our international license if we violate applicable law.

•: Difficulty in predicting change to government regulation, enforcement and interpretation of telecommunications laws. Our business may be harmed if we do not obtain or retain the necessary governmental approval for our services or if we fail to comply with applicable laws. Enforcement and interpretations of these laws and regulations can be unpredictable and are often subject to the informal views of government officials.
•: Changes in access charges and contribution payments. Changes in access charges and contribution payments will affect our cost of providing long distance and other services and could materially and adversely affect our business, financial condition, results of operations and prospects. For 2003, contribution payments were calculated at the rate of 1.3% of our revenues from Canadian telecommunications services.

In the United Kingdom, regulatory considerations that affect or limit our business include the following:

•: The need to comply with laws and regulations. We are subject to the general laws of the United Kingdom including those which relate specifically to telecommunications and to the rules and regulations promulgated thereunder. We are regulated by the Director General of Telecommunications (the "Director General") and the office over which he presides, the Office of Telecommunications ("Oftel"). However, the Director General and Oftel are due to be replaced at the end of 2003 or early in 2004 by a new regulatory authority called the Office of Communications (OFCOM). OFCOM will become the single regulatory authority for the telecommunications and broadcasting sectors. Under the Communications Act adopted July 17, 2003 (the "2003 Act"), all licenses granted previously under the Telecommunications Act 1984 (the "1984 Act") were abolished effective as of July 25, 2003, and we now provide services under and are subject to the terms of a general authorization, which applies to all operators. The Secretary of State has the power to require the suspension of any operator's entitlement to operate under the general authorization in the interests of national security or on public health and safety grounds. Any serious or repeated contravention of the provisions of the general authorization by us would entitle the Director General currently, or OFCOM in the future, to suspend our entitlement to operate under it. Breaches of the general authorization could also result in our incurring financial penalties. We are subject to the views and opinions of, and ultimately to decisions taken by, the Director General currently, and OFCOM in the future, concerning the interpretation of the general authorization and our obligations thereunder and our compliance with the terms of the general authorization.

•: Transition period resulting from recently enacted legislation. The terms of the general authorization have not been finalized in all respects and, in due course, additional provisions will be added. These additions will concern mainly, but not exclusively, operators who are deemed to possess significant market power. We can make no assurances that the general authorization, as finalized or as modified in the future, will not have an adverse impact on our business. Furthermore, although the duties and powers of the Director General currently, and OFCOM in the future, and the provisions which they can insert into the general authorization are prescribed under the 2003 Act, there can be no guarantee that, on specific issues, OFCOM will adopt the same policy approach as was adopted previously by the Director General and Oftel.
•: Administrative Charges. Under the general authorization, we are subject to annual administrative charges based on a formula related to annual revenues. The administrative charges effectively replace the license fees under the prior regime, and we cannot make any assurances that they will not result in higher annual payments by us.
•: Changes in access charges and universal service payments. We must interconnect our United Kingdom network to the networks of other service providers in the United Kingdom, including BT, to allow end user customers to obtain access to our services and to compete effectively in the United Kingdom. Because it has been deemed to possess significant market power, BT is subject to detailed regulation over the pricing of and other terms on which it provides wholesale interconnection services. Without this regulation or with greater pricing flexibility, BT would be able to charge us higher prices for certain services, subject to any constraints imposed by general competition law. Any decision by the Director General currently, or OFCOM in the future, to require us to provide or to contribute to a fund for the provision of a universal service could materially and adversely affect our business.

Risks Related to an Investment in the Notes

Our high level of debt may adversely affect our ability to satisfy our obligations under the notes.

We cannot assure you that we will be able to meet our debt service obligations. A default in our debt obligations, including a breach of any restrictive covenant imposed by the terms of our indebtedness, could result in the acceleration of a substantial portion of our indebtedness. In such a situation, it is unlikely we would be able to fulfill our obligations under the notes or otherwise repay the accelerated indebtedness or make other required payments. Even in the absence of an acceleration of our indebtedness, a default under the terms of our indebtedness could have an adverse impact on our ability to satisfy our debt service obligations, including our obligations under the notes, and on the trading price of the notes and our common stock.

We may not be able to pay interest and principal on the notes if we do not receive distributions from our subsidiaries.

We are a holding company with no operations of our own and no significant assets other than the stock of, and intercompany loans payable by, our operating subsidiaries and cash. Dividends, intercompany loans and other permitted payments from our direct and indirect subsidiaries, and our own credit arrangements, are our sources of funds to meet our cash needs, including the payment of expenses and principal and interest on the notes. Our subsidiaries are legally distinct from us and have no obligations to pay amounts due with respect to the notes or to otherwise make funds available to us. Our subsidiaries will not guarantee the notes. Many of our subsidiaries are organized in jurisdictions outside the United States. Their ability to pay dividends, repay intercompany loans or make other distributions may be restricted by, among other things, the availability of funds, the terms of various credit arrangements entered into by them, as well as statutory and other legal restrictions. Additionally, payments from our subsidiaries may result in adverse tax consequences. If we do not receive dividends,

distributions and other payments from our subsidiaries, we would be restricted in our ability to pay interest and principal on the notes and other indebtedness and in our ability to use cash flow from one subsidiary to cover shortfalls in working capital at another subsidiary.

Our holding company structure may limit your recourse to our subsidiaries' assets.

Creditors of a holding company, such as the holders of the notes, and the holding company itself generally will have subordinate claims against the assets of a particular subsidiary as compared to the creditors of that subsidiary. Accordingly, the notes will be structurally subordinated to all existing and future debt and other liabilities of our subsidiaries, including trade payables. As of June 30, 2003, our subsidiaries had outstanding debt and other liabilities (including trade payables, but excluding intercompany loans) of approximately $475.3 million. Our right to receive assets of any subsidiary upon the liquidation or reorganization of that subsidiary (and the consequent rights of the holders of the notes to participate in those assets) will be structurally subordinated to the claims of that subsidiary's creditors. Even if we are recognized as a creditor of that subsidiary as a result of an intercompany loan, our claims would be subordinate to any secured indebtedness of such subsidiary and any indebtedness of such subsidiary that is senior to our claims. We have no significant assets other than cash and the stock of, and intercompany loans payable by, our subsidiaries. If we or any of our subsidiaries were to enter into a bank credit facility or similar arrangement, we expect that the stock of the subsidiaries would be pledged to secure any such credit facility or arrangement, in which case, any claims you may have as a noteholder against the stock of the subsidiaries would be subordinate to claims of the lenders under such credit facility or arrangement.

Our ability to repurchase notes with cash upon a change of control may be limited.

In certain circumstances involving a change of control of Primus, the holders of the notes may require us to repurchase some or all of the holders' notes. If we are unable to pay some or all of the repurchase price in common stock, we will have to pay such repurchase price in cash. We cannot assure you that we will have sufficient financial resources at such time or would be able to arrange financing to pay the repurchase price of the notes in cash. Our ability to repurchase the notes in cash in such event may be limited by law, by the indenture or by the terms of other agreements. In addition, a change of control may trigger repayment obligations under the terms of our other indebtedness. In such a situation, we would be required to repay our other indebtedness in addition to being required to repurchase the notes at the option of the holders (to the extent we cannot satisfy our repurchase obligations in common stock). We may not have or be able to raise sufficient funds to satisfy all of our repayment or repurchase obligations.

If an active trading market for the notes does not develop, then the market price of the notes may decline or you may not be able to sell your notes.

We cannot assure you that any liquid market will develop for the notes or that holders of the notes will be able to sell their notes, and we cannot provide assurances concerning the price at which the holders will be able to sell their notes. Before this offering, the trading market for the notes has been limited to trading in PORTAL, which terminated as of the date of this prospectus. Although the initial purchasers of the notes have advised us that they intend to make a market in the notes, they are not obligated to do so. The initial purchasers could stop making a market at any time without notice. Accordingly, no market for the notes may develop, and any market that develops may not last. We do not intend to apply for listing of the notes on any securities exchange or other stock market. The liquidity of the trading market and the trading price of the notes may be adversely affected by declines in the trading price of our common stock and our other public debt securities, by changes in our financial performance or prospects and by changes in the financial performance of or prospects for companies in our industry generally.

Transfers of the notes and common stock issuable upon conversion of the notes may be restricted.

We will have the right, pursuant to the registration rights agreement, to suspend the use of the shelf registration statement in certain circumstances. In the event of such a suspension, you would not be able to sell any notes or shares of common stock issuable upon conversion of the notes.

Risks Relating to an Investment in our Common Stock Issuable upon Conversion of the Notes

Future sales of our common stock in the public market could lower our stock price.

Future sales of our common stock in the public market could lower our stock price and impair our ability to raise funds in new stock offerings. As of September 30, 2003, we had 65,521,195 outstanding shares of our common stock that were subject to dilution by:

•: 22,616,990 shares of common stock, subject to potential adjustment, issuable upon conversion of outstanding shares of our Series C convertible preferred stock (the "Series C Preferred");
•: 14,157,925 shares of common stock offered under this prospectus that are also subject to potential adjustment and are issuable upon conversion of the notes;
•: 7,694,895 shares of common stock issuable upon the exercise of outstanding stock options;
•: 1,428,342 shares of common stock issuable upon the conversion of our 5³/4% convertible subordinated debentures due 2007 (the "2007 Notes"); and
•: 333,587 shares of common stock issuable upon the exercise of outstanding warrants issued in connection with the sale of our 11³/4% senior notes due 2004 (the "Warrants").

The 22,616,990 shares of common stock issuable upon conversion of the Series C Preferred will be registered with the Securities and Exchange Commission ("SEC") under the federal securities laws; in addition, the holders of the Series C Preferred, as well as certain other holders of common stock, may require us to register a substantial number of shares of common stock (which consists of, in the case of the Series C Preferred, the common stock issuable upon conversion of the Series C Preferred) for resale, subject to certain limitations. See "Description of Capital Stock—Registration Rights." In addition, 17,725,750 and 4,891,240 shares of common stock underlying the Series C Preferred as of September 30, 2003 become eligible for resale through Rule 144 under the Securities Act on December 31, 2003 and March 31, 2004, respectively. We may also issue a significant number of additional shares of common stock as consideration for future acquisitions or other investments. Sales of a substantial amount of common stock in the public market, or the perception that these sales may occur, could adversely affect the market price of our common stock prevailing from time to time in the public market and could impair our ability to raise funds in additional stock offerings.

The market price of our common stock may decline and fluctuate significantly.

In recent years, the market prices for securities of companies in the telecommunications industry have declined substantially and have been highly volatile. For example, from January 1, 1998 through December 31, 1999, the market price of our common stock and the Standard & Poor's Telecommunications (Long Distance) Index (the Long Distance Index) increased by 137% and 110%, respectively. Subsequently, from January 1, 2000 through September 30, 2003, the market price of our common stock and the Long Distance Index declined by 82% and 89%, respectively. Various factors and events may cause the market price of our common stock to decline or fluctuate significantly. Such factors and events include the liquidity of the market for our common stock, variations in our quarterly operating results and our growth strategies, regulatory, technological or other changes (both domestic and international) affecting the telecommunications industry generally, our competitors' business developments, changes in the cost of telecommunications service or other operating costs and changes in general market conditions. On May 14, 2002, our common stock was delisted from the Nasdaq

National Market for failure to meet the required minimum bid price necessary to maintain listing on the Nasdaq National Market, and on such date our common stock began trading on the Nasdaq SmallCap Market, which is generally a less liquid market than the Nasdaq National Market. On March 21, 2003, the listing of our common stock on the Nasdaq National Market was reinstated, after once again satisfying the minimum bid price requirements. There can be no assurance that our common stock will not decline or that future declines in the market price of our common stock will not result in our common stock being delisted from the Nasdaq National Market again or that if such delisting does occur, that there would be a liquid market for our common stock.

A small group of our stockholders could exercise influence over our affairs.

As of September 30, 2003, there were 559,950 shares of our Series C Preferred issued and outstanding. Based on the conversion ratio of 40.3911 shares of common stock as of September 30, 2003 for each share of the Series C Preferred and the number of shares of common stock outstanding as of September 30, 2003, the outstanding Series C Preferred was convertible into 22,616,990 shares of common stock, or 25.66% of our outstanding common stock, on an as-converted basis. Subject to the maintenance of certain minimum ownership levels, the holders of the Series C Preferred have certain governance rights not granted to holders of our common stock, such as:

•: the right to elect one member to the board of directors (so long as the holders of Series C Preferred maintain at least a 5% ownership interest in us);
•: the right to participate in certain future equity issuances;
•: certain protective provisions described under "Description of Capital Stock—Series C Preferred" that require the consent of the Series C Preferred or the consent of a majority of the director nominated by the Series C Preferred and our other non-interested directors acting as a group before we may undertake certain actions; and
•: certain price-based anti-dilution protection.

Furthermore, the holders of the Series C Preferred have a right to receive dividends and liquidation preference payments ahead of the holders of our common stock. As of September 30, 2003, funds affiliated with American International Group, Incorporated (AIG) owned 95.23% of our outstanding Series C Preferred, which in turn represents 24.44% of the outstanding common stock on an as-converted basis. In addition to the protective provisions described above, the Series C Preferred votes with the common stockholders on an as-converted basis. As a result, AIG could exercise significant influence over such matters as:

•: the election of our directors;
•: amendments to our certificate of incorporation;
•: other fundamental corporate transactions such as mergers and asset sales; and
•: the general direction of our business and affairs.

In addition, the applicable triggering provisions of our Rights Agreement (described in greater detail below and under "Description of Capital Stock—Takeover Protections—Rights Agreement") contain exceptions with respect to the acquisition of beneficial ownership of our shares by holders of the Series C Preferred. As a result, holders of the Series C Preferred could gain additional control over our affairs without triggering the provisions of our Rights Agreement.

Anti-takeover provisions could impede or discourage a third party acquisition.

We are a Delaware corporation and the anti-takeover provisions of Delaware law impose various impediments to the ability of a third party to acquire control of our company, even if a change in

control would be beneficial to our existing stockholders. In addition, our board of directors has the power, without stockholder approval, to designate the terms of one or more series of preferred stock and issue shares of preferred stock, which could be used defensively if a takeover is threatened. We also have adopted a Rights Agreement, commonly known as a "poison pill," that entitles our stockholders to acquire additional shares of our common stock, or a potential acquirer of our company, at a substantial discount from their market value in the event of an attempted takeover, unless such stockholders' rights are earlier redeemed or exchanged by us in the discretion of our board of directors. Our by-laws provide for a classified board of directors serving staggered three-year terms and restrictions on who may call a special meeting of stockholders, and our certificate of incorporation prohibits stockholder action by written consent. The indentures governing our outstanding notes and public debt require that we offer to repurchase such debt or notes upon a change of control. Lastly, all options issued under our stock option plans automatically vest upon a change of control. Our incorporation under Delaware law, our board of directors' ability to create and issue a new series of preferred stock, the acceleration of the vesting of options, the existence of our Rights Agreement, the requirement to repurchase senior notes and the notes, and certain provisions of our certificate of incorporation or by-laws could impede a merger, takeover or other business combination involving our company or discourage a potential acquirer from making a tender offer for our common stock, which, under certain circumstances, could reduce the market value of our common stock. See "Description of Capital Stock—Takeover Protections."

USE OF PROCEEDS

We will not receive any proceeds from the sale of the notes or the shares of common stock offered by this prospectus. See "Selling Security Holders."

DIVIDEND POLICY

We have not paid any cash dividends on our common stock to date. The payment of dividends, if any, in the future is within the discretion of our board of directors and will depend on our earnings, capital requirements and financial condition. Dividends are also restricted by certain of the indentures governing our outstanding notes and may be restricted by other credit arrangements entered into in the future. See "Risks Related to an Investment in the Notes—We may not be able to pay interest and principal on the notes if we do not receive distributions from our subsidiaries." Our board of directors presently intends to retain all earnings, if any, for use in our business operations, and accordingly, our board of directors does not expect to declare or pay any dividends in the foreseeable future.

The holders of our Series C Preferred have the right to receive preferential non-cumulative dividends, if and when declared by our board of directors, at an annual rate of 8% of the per share purchase price of the Series C Preferred. Any such dividends declared by the Board may be paid at the discretion of the Board in cash, in shares of our common stock or by any combination of cash or shares. Common stock paid as a dividend will be valued at the average daily closing price of our common stock during the consecutive 30-day trading period ending on the applicable dividend date. These dividends are payable prior to any dividend to be paid on any other class of our capital stock, including our common stock.

SELECTED FINANCIAL DATA

The following selected financial data should be read in conjunction with our consolidated and consolidated condensed financial statements, the notes thereto, and with "Management's Discussion and Analysis of Financial Condition and Results of Operations" contained in documents incorporated by reference into this prospectus. The statement of operations data for the years ended December 31, 1998, 1999, 2000, 2001 and 2002 and the balance sheet data as of December 31, 1998, 1999, 2000, 2001 and 2002 have been derived from our consolidated financial statements, which have been audited by Deloitte & Touche LLP, independent auditors. The statement of operations data for the six months ended June 30, 2002 and 2003, and the balance sheet data as of June 30, 2002 and 2003, have been derived from the unaudited consolidated condensed financial statements which, in management's opinion, include all adjustments (consisting of only normal recurring adjustments) necessary for a fair presentation of the information set forth therein. You should not rely on interim results as being indicative of results we may expect for the full year.

			Year Ended December 31,															Six Months Ended June 30,
			1998			1999			2000			2001			2002			2002			2003
			(in thousands, except per share amounts)
Statement of Operations Data:
Net revenue			$	421,628		$	832,739		$	1,199,422		$	1,082,475		$	1,024,056		$	495,911		$	620,683
Cost of revenue				353,016			624,599			861,181			767,841			668,643			327,462			386,386

Gross margin				68,612			208,140			338,241			314,634			355,413			168,449			234,297

Operating expenses
	Selling, general and administrative			79,532			199,581			330,411			303,026			254,152			123,514			166,866
	Depreciation and amortization			24,185			54,957			120,695			157,596			82,239			39,971			41,553
	Loss on sale of assets			—			—			—			—			—			—			804
	Asset impairment write-down			—			—			—			526,309			22,337			337			537

		Total operating expenses		103,717			254,538			451,106			986,931			358,728			163,822			209,760

Income (loss) from operations				(35,105	)		(46,398	)		(112,865	)		(672,297	)		(3,315	)		4,627			24,537
Interest expense				(40,047	)		(79,629	)		(132,137	)		(100,700	)		(68,303	)		(34,523	)		(29,999	)
Gain on early extinguishment of debt				—			—			40,952			491,771			36,675			27,251			14,634
Interest income and other income (expense)				11,504			13,395			30,743			(17,951	)		(771	)		875			200
Foreign currency transaction gain (loss)				—			(104	)		(1,357	)		(1,999	)		8,486			282			24,818

Income (loss) before income taxes				(63,648	)		(112,736	)		(174,664	)		(301,176	)		(27,228	)		(1,488	)		34,190
Income tax benefit (expense)				—			—			—			(5,000	)		3,598			10,668			(2,953	)

Income (loss) before cumulative effect of change in accounting principle				(63,648	)		(112,736	)		(174,664	)		(306,176	)		(23,630	)		9,180			31,237
Cumulative effect of change in accounting principle				—			—			—			—			(10,973	)		(10,973	)		—

Net income (loss)				(63,648	)		(112,736	)		(174,664	)		(306,176	)		(34,603	)		(1,793	)		31,237
Accreted and deemed dividend on convertible preferred stock				—			—			—			—			—			—			(1,678	)

Income (loss) attributable to common stockholders			$	(63,648	)	$	(112,736	)	$	(174,664	)	$	(306,176	)	$	(34,603	)	$	(1,793	)	$	29,559

Basic income (loss) per common share			$	(2.61	)	$	(3.72	)	$	(4.40	)	$	(5.73	)	$	(0.54	)	$	(0.03	)	$	0.35

Diluted income (loss) per common share			$	(2.61	)	$	(3.72	)	$	(4.40	)	$	(5.73	)	$	(0.54	)	$	(0.03	)	$	0.34

Weighted average shares outstanding:
	Basic			24,432			30,323			39,691			53,423			64,631			64,367			85,332
	Diluted			24,432			30,323			39,691			53,423			64,631			64,367			87,572

		Year Ended December 31,															Six Months Ended June 30,
		1998			1999			2000			2001			2002			2002			2003
		(in thousands, except ratios)
Geographic Data
Net revenue:
	North America	$	188,008		$	406,083		$	533,027		$	453,111		$	381,569		$	185,802		$	237,764
	Europe		60,863			195,477			358,986			357,047			363,669			175,156			219,185
	Asia-Pacific		172,757			231,179			307,409			272,317			278,818			134,953			163,734

Total		$	421,628		$	832,739		$	1,199,422		$	1,082,475		$	1,024,056		$	495,911		$	620,683

Other Data:
Gross margin as a percentage of net revenue			16.3%			25.0%			28.2%			29.1%			34.7%			34.0%			37.7%
Capital expenditures		$	75,983		$	110,582		$	193,772		$	87,771		$	29,367		$	13,350		$	9,677
Ratio of earnings to fixed charges(1)			<0			<0			<0			<0			<0			<0			2.07
Free Cash Flow(2):
Net cash provided by (used in) operating activities		$	(71,296	)	$	(55,570	)	$	(131,020	)	$	(110,351	)	$	34,633		$	6,643		$	39,154
Net cash used in investing activities			(54,221	)		(200,173	)		(240,014	)		(89,355	)		(31,607	)		(13,698	)		(10,806	)

Free cash flow		$	(125,517	)	$	(255,743	)	$	(371,034	)	$	(199,706	)	$	3,026		$	(7,055	)	$	28,348

	as of December 31,												as of June 30,
	1998		1999		2000		2001			2002			2002			2003
	(in thousands)
Balance Sheet Data:
Cash and cash equivalents	$	136,196	$	471,542	$	393,812	$	83,953		$	92,492		$	62,196		$	65,776
Restricted cash and investments	$	25,729	$	25,932	$	5,066	$	4,961		$	11,712		$	5,463		$	11,958
Working capital(3)	$	107,193	$	384,998	$	255,436	$	(62,590	)	$	(64,771	)	$	(77,943	)	$	(98,803	)
Total assets	$	673,963	$	1,450,746	$	1,748,126	$	816,214		$	724,588		$	778,688		$	734,729
Long-term obligations (including current portion)	$	420,174	$	929,944	$	1,256,453	$	667,587		$	600,988		$	614,635		$	541,978
Stockholder's equity (deficit)	$	114,917	$	190,859	$	83,695	$	(178,484	)	$	(200,123	)	$	(163,342	)	$	(127,381	)

(1): The ratio of earnings to fixed charges is computed by dividing pre-tax income from continuing operations (before adjustment for minority interests in consolidated subsidiaries and loss from equity investees) by fixed charges. Fixed charges consist of interest charges, whether expensed or capitalized, and that portion of rental expense we believe to be representative of interest. For the years ended December 31, 1998, 1999, 2000, 2001 and 2002 and the six months ended June 30, 2002, earnings were insufficient to cover fixed charges by $63.6 million, $112.4 million, $174.6 million, $301.0 million, $23.6 million and $1.1 million, respectively. For the six-month period ended June 30, 2003, after giving pro forma effect to a net decrease in interest expense resulting from the assumed application of proceeds from the September 15, 2003 offering of the notes as of January 1, 2003, the ratio of earnings to fixed charges was 2.33.
(2): Free cash flow, as defined by us, consists of net cash provided by (used in) operating activities less net cash used in investing activities. Free cash flow, as defined above, may not be similar to free cash flow measures presented by other companies, is not a measurement under generally accepted accounting principles in the United States, and should be considered in addition to, but not as a substitute for, the information contained in our statement of cash flows. We believe free cash flow provides a measure of our ability, after making our capital expenditures and other investments in our infrastructure, to meet scheduled debt payments. We use free cash flow to monitor the impact of our operations on our cash reserves and our ability to generate sufficient cash flow to fund our scheduled debt maturities and other financing activities, including discretionary refinancings and retirements of debt. Because free cash flow represents the amount of cash generated or used in operating activities and investing activities before deductions for scheduled debt maturities and other fixed obligations (such as capital leases, vendor financing and other long-term obligations), you should not use it as a measure of the amount of cash available for discretionary expenditures. Scheduled debt maturities paid during the years ended December 31, 1998, 1999, 2000, 2001 and 2002 were $2.4 million, $21.9 million, $16.3 million, $33.7 million and $25.9 million, respectively and during the six months ended June 30, 2002 and June 30, 2003 were $21.2 million and $31.5 million, respectively. For information regarding our scheduled debt maturities and other fixed obligations, you should review the table disclosing our long-term obligations under "Management's Discussion and Analysis of Financial Conditions and Results of Operations—Liquidity—Short-and Long-Term Liquidity Considerations and Risks incorporated by reference into this prospectus from our quarterly and annual reports on Form 10-Q and 10-K, as filed with the SEC. See "Where You Can Find More Information."
(3): Working capital consists of current assets less current liabilities, in each case calculated in accordance with United States generally accepted accounting principles. The decrease in working capital as of June 30, 2003 as compared to December 31, 2002 is primarily a result of our using the cash received from the issuance of the Series C Preferred to reduce long-term debt in the amount of $42.5 million.

DESCRIPTION OF THE NOTES

We issued the notes under an indenture, dated as of September 15, 2003, between us and Wachovia Bank, National Association, as trustee. The terms of the notes include those provided in the indenture, the notes and those provided in the registration rights agreement, which we entered into with the initial purchasers. The following description is only a summary of the material provisions of the notes, the indenture, and the registration rights agreement related to the notes. We urge you to read these documents in their entirety because they, and not this description, will define your rights as holders of these notes. You may request copies of these documents at our address set forth above under the caption "Summary."

When we refer to Primus, "we", "our" or "us" in this section, we refer only to Primus Telecommunications Group, Incorporated, a Delaware corporation, and not its subsidiaries.

Brief Description of the Notes

The notes are:

•: limited to $132.0 million in aggregate principal amount;
•: senior unsecured obligations, ranking equally with all of our existing and future senior debt and senior in right of payment to all of our existing and future subordinated debt, but as debt of Primus, the notes are effectively subordinated to all of our existing and future secured debt to the extent of the value of the collateral securing such debt and structurally subordinated to all existing and future debt and other liabilities of our subsidiaries;
•: convertible into our common stock at an initial conversion price of $9.3234 per share, subject to adjustment as described below under "—Conversion Rights";
•: subject to repurchase at your option if a change of control occurs as set forth below under "—Repurchase at Option of Holders Upon a Change of Control"; and
•: due on September 15, 2010 unless earlier converted or repurchased, at your option, upon a change of control.

The indenture does not contain any financial covenants and does not restrict us or our subsidiaries from paying dividends, incurring additional debt or issuing or repurchasing our other securities. In addition, the indenture does not protect you in the event of a highly leveraged transaction or a change in control of Primus except to the extent described below under "—Repurchase at Option of Holders Upon a Change of Control."

No sinking fund is provided for the notes. The notes are not subject to defeasance. The notes have been issued only in registered form in denominations of $1,000 and any integral multiple of $1,000 above that amount. No service charge will be made for any registration of transfer or exchange of notes, but we may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith.

You may present definitive notes for conversion, registration of transfer and exchange, without service charge, at our office or agency in New York City, which shall initially be the office or agency of the trustee in New York City. For information regarding conversion, registration of transfer and exchange of global notes, see "—Form, Denomination and Registration."

Ranking

The notes are our senior unsecured obligations and rank equally in right of payment with all of our existing and future senior debt and senior in right of payment to all of our existing and future

subordinated debt. The notes are effectively subordinated to all of our existing and future secured debt to the extent of the value of the collateral securing such debt.

As of June 30, 2003, we had $315.7 million (excluding debt of our subsidiaries) of outstanding senior debt and $71.1 million (excluding debt of our subsidiaries) of outstanding subordinated debt.

We are a holding company with no operations of our own and no significant assets other than cash and the stock of, and intercompany loans payable by, our operating subsidiaries. Dividends, intercompany loans and other permitted payments from our direct and indirect subsidiaries, and our own credit arrangements, are our sources of funds to meet our cash needs, including the payment of expenses and principal and interest on the notes. Our subsidiaries are legally distinct from us and have no obligations to pay amounts due with respect to the notes or to otherwise make funds available to us. Claims of creditors of such subsidiaries generally will have priority with respect to assets of such subsidiaries over the claims of our creditors, including holders of the notes. Accordingly, the notes are structurally subordinated to all existing and future debt and other liabilities of our subsidiaries, including trade payables. As of June 30, 2003, our subsidiaries had $475.3 million of outstanding debt and other liabilities, including trade payables but excluding intercompany liabilities, all of which are structurally senior to the notes.

Interest

The notes bear interest from September 15, 2003 at the rate of 3³/4% per year. We will pay interest semiannually in arrears on March 15 and September 15 of each year to the holders of record at the close of business on the preceding March 1 and September 1, respectively, beginning March 15, 2004. There are two exceptions to the preceding sentence:

•: In general, we will not pay accrued and unpaid interest on any note that is converted into our common stock. See "—Conversion Rights—Conversion Procedures"; and
•: We will pay interest to a person other than the holder of record on the relevant record date if holders elect to require us to repurchase the notes on a date that is after the record date and on or prior to the corresponding interest payment date. In this instance, we will pay accrued and unpaid interest on the notes being repurchased to, but excluding, the repurchase date, to the same person to whom we will pay the principal of those notes.

We will pay the principal of, interest on, and any additional amounts due in respect of the global notes to DTC in immediately available funds.

In the event definitive notes are issued, we will pay interest and any additional amounts due on:

•: definitive notes having an aggregate principal amount of $5.0 million or less by check mailed to the holders of those notes;
•: definitive notes having an aggregate principal amount of more than $5.0 million by wire transfer in immediately available funds if requested by holder of those notes; and
•: at maturity, we will pay the principal of and interest on the definitive notes at our office or agency in New York City, which initially will be the office or agency of the trustee in New York City.

Interest generally will be computed on the basis of a 360-day year comprised of twelve 30-day months.

Conversion Rights

General

You may convert any outstanding notes (or portions of outstanding notes) into our common stock, initially at the conversion price of $9.3234 per share, equal to a conversion rate of 107.257 shares per $1,000 principal amount of notes. The conversion price is subject, however, to adjustment as described below under "—Conversion Price Adjustments." We will not issue fractional shares of common stock upon conversion of notes. Instead, we will pay cash to you in an amount equal to the market value of that fractional share based upon the closing sale price of our common stock on the trading day immediately preceding the conversion date. You may convert notes only in denominations of $1,000 and whole multiples of $1,000.

You may exercise conversion rights at any time prior to the close of business on the business day prior to the final maturity date of the notes. However, if you have exercised your right to require us to repurchase your notes because a change of control has occurred, you may convert your notes into our common stock only if you withdraw your notice and convert your notes prior to the close of business on the second business day immediately preceding the change of control repurchase date.

Conversion Procedures

Except as provided below, if you convert your notes into our common stock on any day other than an interest payment date, you will not receive any interest that has accrued on these notes since the prior interest payment date. By delivering to the holder the number of shares issuable upon conversion, determined by dividing the principal amount of the notes being converted by the conversion price, together with a cash payment, if any, in lieu of fractional shares, we will satisfy our obligation with respect to the converted notes. That is, accrued but unpaid interest will be deemed to be paid in full rather than canceled, extinguished or forfeited.

If you convert after a record date for an interest payment but prior to the corresponding interest payment date, you will receive on the interest payment date interest accrued and paid on such notes, notwithstanding the conversion of such notes prior to such interest payment date, because you will have been the holder of record on the corresponding record date. However, at the time you surrender such notes for conversion, you must pay us an amount equal to the interest that has accrued and will be paid on the notes being converted on the interest payment date.

You will not be required to pay any transfer taxes or duties relating to the issuance or delivery of our common stock if you exercise your conversion rights, but you will be required to pay any transfer tax or duties which may be payable relating to any transfer involved in the issuance or delivery of the common stock in a name other than yours. Certificates representing shares of common stock will be issued or delivered only after all applicable transfer taxes and duties, if any, payable by you have been paid.

To convert interests in a global note, you must deliver to DTC the appropriate instruction form for conversion pursuant to DTC's conversion program.

To convert a definitive note, you will be required to:

•: complete the conversion notice on the back of the note (or a facsimile of it);
•: deliver the completed conversion notice and the notes to be converted to the specified office of the conversion agent;
•: pay all funds required, if any, relating to interest on the notes to be converted to which you are not entitled, as described in the second preceding paragraph; and
•: pay all transfer taxes or duties, if any, as described in the preceding paragraph.

The conversion date will be the date on which all of the foregoing requirements have been satisfied. The notes will be deemed to have been converted immediately prior to the close of business on the conversion date. We will deliver, or cause to be delivered, to you a certificate for the number of shares of common stock into which the notes are converted (and cash in lieu of any fractional shares) as soon as practicable on or after the conversion date.

Conversion Price Adjustments

We will adjust the initial conversion price for certain events, including:

(1)

issuances of our common stock as a dividend or distribution on our common stock;

(2)

certain subdivisions, combinations or reclassifications of our common stock;

(3)

issuances to all or substantially all holders of our common stock of certain rights or warrants to purchase our common stock (or securities convertible into our common stock) at less than (or having a conversion price per share less than) the current market price of our common stock;

(4)

distributions to all or substantially all holders of our common stock of shares of our capital stock (other than our common stock), evidences of our indebtedness or assets, including securities, but excluding:

•: any dividends and distributions in connection with a reclassification, consolidation, merger, statutory share exchange, combination, sale or conveyance resulting in a change in the conversion consideration pursuant to the fifth succeeding paragraph;
•: any dividends or distributions paid exclusively in cash; or

(5)

dividends or other distributions consisting exclusively of cash to all or substantially all holders of our common stock, excluding dividends or distributions made in connection with our liquidation, dissolution or winding-up; and

(6)

purchases of our common stock pursuant to a tender offer or exchange offer made by us or any of our subsidiaries (excluding offers for stock options, warrants or similar instruments and the common stock underlying such instruments) to the extent that the aggregate value of the cash and any other consideration included in the payment, together with:

•: any cash and the fair market value of other consideration payable in a tender offer or exchange offer by us or any of our subsidiaries for our common stock expiring within the 365-day period preceding the expiration of that tender offer or exchange offer in respect of which no adjustments have been made; and
•: the aggregate amount of any cash distributions to all holders of our common stock within the 365-day period preceding the expiration of that tender offer or exchange offer in respect of which no adjustments have been made,

exceeds 5% of our market capitalization on the expiration date of such tender offer.

We have issued Rights (as defined in "Description of Capital Stock—Takeover Protections—Rights Agreement") to all holders of our common stock pursuant to our Rights Agreement described under "Description of Capital Stock—Takeover Protections—Rights Agreement." If any holder converts notes prior to the Rights trading separately from the common stock, the holder will become entitled to receive Rights in addition to the common stock. Following a Distribution Date (as defined in "Description of Capital Stock—Takeover Protections—Rights Agreement"), the conversion ratio will be adjusted. If such an adjustment is made and the Rights are later redeemed, invalidated or terminated, then a reversing adjustment will be made.

We will not make any adjustment if holders may participate in the transaction or in certain other cases. In cases where the fair market value of assets, debt securities or certain rights, warrants or options to purchase our securities, applicable to one share of common stock, distributed to stockholders:

•: equals or exceeds the average closing price of the common stock over the ten consecutive trading day period ending on the record date for such distribution, or
•: such average closing price exceeds the fair market value of such assets, debt securities or rights, warrants or options so distributed by less than $1.00,

rather than being entitled to an adjustment in the conversion price, the holder of a note will be entitled to receive upon conversion, in addition to the shares of common stock, the kind and amount of assets, debt securities or rights, warrants or options comprising the distribution that such holder would have received if such holder had converted such notes immediately prior to the record date for determining the shareholders entitled to receive the distribution.

We will not make an adjustment in the conversion price unless such adjustment would require a change of at least 1% in the conversion price then in effect at such time. We will carry forward and take into account in any subsequent adjustment any adjustment that would otherwise be required to be made. Except as stated above, we will not adjust the conversion price for the issuance of our common stock or any securities convertible into or exchangeable for our common stock or carrying the right to purchase any of the foregoing.

If we distribute shares of capital stock of a subsidiary, the conversion price will be adjusted, if at all, based on the market value of the subsidiary stock so distributed relative to the market value of our common stock, in each case over a measurement period following the distribution, unless we elect to reserve the pro rata portion of such shares for the benefit of the holders of notes.

If we:

•: reclassify or change our common stock (other than changes resulting from a subdivision or combination), or
•: consolidate or combine with or merge into any person or sell or convey to another person all or substantially all of our property and assets,

and the holders of our common stock receive stock, other securities or other property or assets (including cash or any combination thereof) with respect to or in exchange for their common stock, each outstanding note would, without the consent of any holders of notes, become convertible only into the consideration the holders of notes would have received if they had converted their notes immediately prior to such reclassification, change, consolidation, merger, statutory share exchange, combination, sale or conveyance.

If a taxable distribution to holders of our common stock or other transaction occurs which results in any adjustment of the conversion price (including an adjustment at our option), you may, in certain circumstances, be deemed to have received a distribution subject to U.S. income tax as a dividend. In certain other circumstances, the absence of an adjustment may result in a taxable dividend to the holders of our common stock. See "Material United States Federal Income Tax Consequences."

We may from time to time, to the extent permitted by law, reduce the conversion price of the notes by any amount for any period of at least 20 days. In that case, we will give at least 15 days prior notice of such decrease. We may make such reductions in the conversion price, in addition to those set forth above, as our board of directors deems advisable to avoid or diminish any income tax to holders of our common stock resulting from any dividend or distribution of stock (or rights to acquire stock) or from any event treated as such for income tax purposes.

If we adjust the conversion price pursuant to the above provisions, we will issue a press release through Dow Jones & Company, Inc. or Bloomberg Business News containing the relevant information and make this information available on our web site or through another public medium as we may use at that time.

Repurchase at Option of Holders Upon a Change of Control

Repurchase Upon a Change of Control

If a change of control occurs, holders may require us to repurchase all of their notes, or any portion of those notes that is equal to $1,000 or a whole multiple of $1,000, at a repurchase price equal to 100% of the principal amount of the notes to be repurchased plus any accrued and unpaid interest to, but excluding, the repurchase date.

At our option, instead of paying the repurchase price in cash, we may pay the repurchase price in our common stock, the common stock of the acquiring company or its parent, or a combination of cash and such common stock, valued at 95% of the average of the closing sales prices of such common stock on the Nasdaq National Market, or the principal national securities exchange on which such common stock is listed, for the five consecutive trading days ending on the third trading day prior to the repurchase date. We may not pay the repurchase price in common stock unless we satisfy certain conditions provided in the indenture.

A "change of control" will be deemed to have occurred at such time after the original issuance of the notes when any of the following has occurred:

•

the acquisition by any person, including any syndicate or group deemed to be a "person" under Section 13(d)(3) of the Exchange Act, of beneficial ownership, directly or indirectly, through a purchase, merger or other acquisition transaction or series of purchases, mergers or other acquisition transactions of shares of our capital stock entitling that person to exercise 50% or more of the total voting power of all shares of our capital stock entitled to vote generally in elections of directors, other than any acquisition by us, any of our subsidiaries or any of our employee benefit plans; or

•

the first day on which a majority of the members of our board of directors does not consist of continuing directors; or

•

the consolidation or merger of us with or into any other person, any merger of another person into us, or any conveyance, transfer, sale, lease or other disposition of all or substantially all of our properties and assets to another person, other than:

(1)

any transaction:

•: that does not result in any reclassification, conversion, exchange or cancellation of outstanding shares of our capital stock; and
•: pursuant to which the holders of 50% of more of the total voting power of all shares of our capital stock entitled to vote generally in elections of directors immediately prior to such transaction have the right to exercise, directly or indirectly, 50% or more of the total voting power of all shares of our capital stock entitled to vote generally in elections of directors of the continuing or surviving person immediately after giving effect to such issuance; and

(2)

any merger primarily for the purpose of changing our jurisdiction of incorporation and resulting in a reclassification, conversion or exchange of outstanding shares of common stock solely into shares of common stock of the surviving entity.

However, a change of control will be deemed not to have occurred if:

•: the closing sale price per share of our common stock for any five trading days within:
•: the period of 10 consecutive trading days ending immediately after the later of the change of control or the public announcement of the change of control, in the case of a change of control under the first or second bullet point above; or
•: the period of 10 consecutive trading days ending immediately before the change of control, in the case of a change of control under the third bullet point above,

equals or exceeds 110% of the conversion price of the notes in effect on each such trading day; or

•: at least 90% of the consideration in the transaction or transactions (other than cash payments for fractional shares and cash payments made in respect of dissenters' appraisal rights) constituting a change of control consists of shares of common stock traded or to be traded immediately following such change of control on a national securities exchange or the Nasdaq Stock Market and, as a result of the transaction or transactions, the notes become convertible solely into such common stock (and any rights attached thereto).

Beneficial ownership shall be determined in accordance with Rules 13d-3 and 13d-5 under the Exchange Act (except that a person shall be deemed to have beneficial ownership of all securities that such person has the right to acquire, whether such right is currently exercisable or is exercisable only upon the occurrence of a subsequent condition). The term "person" includes any syndicate or group which would be deemed to be a "person" under Section 13(d)(3) under the Exchange Act.

"Continuing directors" means, as of any date of determination, any member of the board of directors of Primus who:

•: was a member of the board of directors on the date of this prospectus; or
•: was nominated for election or elected to the board of directors with the approval of a majority of the continuing directors who were members of the board of directors at the time of the new director's nomination or election.

The definition of "change of control" includes a phrase relating to the conveyance, transfer, sale, lease or disposition of "all or substantially all" of our properties and assets. There is no precise, established definition of the phrase "substantially all" under applicable law. In interpreting this phrase, courts, among other things, make a subjective determination as to the portion of assets conveyed, considering many factors, including the value of assets conveyed, the proportion of an entity's income derived from the assets conveyed and the significance of those assets to the ongoing business of the entity. To the extent the meaning of such phrase is uncertain, uncertainty will exist as to whether or not a change of control may have occurred and, accordingly, as to whether or not the holders of notes will have the right to require us to repurchase their notes.

Repurchase Right Procedures

Within 30 days after the occurrence of a change of control, we will be required to give notice to all holders of the occurrence of the change of control and of their resulting repurchase right. The repurchase date will be no later than 30 days after the date we give that notice. The notice will be delivered to the holders at their addresses shown in the register of the registrar and to beneficial owners as required by applicable law, stating, among other things, the procedures that holders must follow to require us to repurchase their notes as described below.

If holders have the right to cause us to repurchase their notes as described above, we will issue a press release through Dow Jones & Company, Inc. or Bloomberg Business News containing the relevant information and make this information available on our web site or through another public medium as we may use at that time.

To elect to require us to repurchase notes, each holder must deliver the repurchase notice so that it is received by the paying agent no later than the close of business on the second business day immediately prior to the repurchase date, unless we specify a later date, and must state certain information, including:

•: the certificate numbers of the holders' notes to be delivered for repurchase;
•: the portion of the principal amount of notes to be repurchased, which must be $1,000 or an integral multiple of $1,000; and
•: that the notes are to be repurchased by us pursuant to the applicable provision of the indenture.

A holder may withdraw any repurchase notice by delivering a written notice of withdrawal to the paying agent prior to the close of business on the repurchase date. The notice of withdrawal must state certain information, including:

•: the principal amount of notes being withdrawn;
•: the certificate numbers of the notes being withdrawn; and
•: the principal amount, if any of the notes that remain subject to the repurchase notice.

The Exchange Act requires the dissemination of certain information to security holders and that an issuer follow certain procedures if an issuer tender offer occurs, which requirements may apply if the repurchase right summarized above becomes available to holders of the notes. In connection with any offer to require us to repurchase notes as summarized above we will, to the extent applicable:

•: comply with the provisions of Rule 13e-4, Rule 14e-1 and any other tender offer rules under the Exchange Act which may then be applicable; and
•: file a Schedule TO or any other required schedule or form under the Exchange Act.

Our obligation to pay the repurchase price for notes for which a repurchase notice has been delivered and not validly withdrawn is conditioned upon the holder delivering the notes, together with necessary endorsements, to the paying agent at any time after delivery of the repurchase notice. We will cause the repurchase price for the notes to be paid promptly following the later of the repurchase date or the time of delivery of the notes, together with such endorsements.

If the paying agent holds money and/or shares of common stock sufficient to pay the repurchase price of the notes for which a repurchase notice has been given on the business day following the repurchase date in accordance with the terms of the indenture, then, immediately after the repurchase date, the notes will cease to be outstanding and interest on the notes will cease to accrue, whether or not the notes are delivered to the paying agent. Thereafter, all other rights of the holder shall terminate, other than the right to receive the repurchase price upon delivery of the notes.

We may, to the extent permitted by applicable law and the agreements governing any of our other indebtedness at the time outstanding, at any time purchase the notes in the open market or by tender at any price or by private agreement. Any notes so purchased by us shall be surrendered to the trustee for cancellation. Any notes surrendered to the trustee may, to the extent permitted by applicable law, be reissued or resold or may be surrendered to the trustee for cancellation. Any note surrendered to the trustee for cancellation may not be reissued or resold and will be canceled promptly.

Limitations on Repurchase Rights

The repurchase rights described above may not necessarily protect holders of the notes if a highly leveraged or another transaction involving us occurs that may adversely affect holders.

Our ability to repurchase notes upon the occurrence of a change of control is subject to important limitations. The occurrence of a change of control could cause an event of default under, or be prohibited or limited by, the terms of our existing or future debt. Further, we cannot assure you that, in that event, we would have the financial resources, or would be able to arrange financing, to pay the repurchase price in cash for all the notes that might be delivered by holders of notes seeking to exercise the repurchase right. In addition, although the terms of the notes allow us to use common stock to repay the repurchase price, we may not be in a position to do so. Any failure by us to repurchase the notes when required following a change of control would result in an event of default under the indenture. Any such default may, in turn, cause a default under our other indebtedness that may be outstanding at that time. In addition, our ability to repurchase notes may be limited by restrictions on our ability to obtain funds for such repurchase through dividends from our subsidiaries and other provisions in agreements that may govern our other indebtedness outstanding at the time.

The change of control repurchase provision of the notes may, in certain circumstances, make more difficult or discourage a takeover of our company. The change of control repurchase feature, however, is not the result of our knowledge of any specific effort by others to accumulate shares of our common stock or to obtain control of us by means of a merger, tender offer solicitation or otherwise or by management to adopt a series of antitakeover provisions. Instead, the change of control purchase feature is a standard term contained in convertible securities similar to the notes.

Consolidation, Merger, Etc.

The indenture provides that we may, without the consent of the holders of any of the notes, consolidate with or merge into any other person or convey, transfer, sell, lease or otherwise dispose of all or substantially all of our properties and assets to another person as long as, among other things:

•: the resulting, surviving or transferee person is organized and existing under the laws of the United States, any state thereof or the District of Columbia;
•: that person assumes all of our obligations under the indenture and the notes; and
•: we or such successor is not then or immediately thereafter in default under the indenture and no event which, after notice or lapse of time, would become an event of default under the indenture, shall have occurred and be continuing.

The occurrence of certain of the foregoing transactions could also constitute a change of control under the indenture.

The covenant described above includes a phrase relating to the conveyance, transfer, sale, lease or disposition of "all or substantially all" of our properties and assets. There is no precise, established definition of the phrase "substantially all" under applicable law. In interpreting this phrase, courts, among other things, make a subjective determination as to the portion of assets conveyed, considering many factors, including the value of assets conveyed, the proportion of an entity's income derived from the assets conveyed and the significance of those assets to the ongoing business of the entity. To the extent the meaning of such phrase is uncertain, uncertainty will exist as to whether or not the restrictions on the sale, lease or disposition of our assets described above apply to a particular transaction.

Events of Default

Each of the following will constitute an event of default under the indenture:

(1)

our failure to pay when due the principal of any of the notes at maturity or upon exercise of a repurchase right or otherwise;

(2)

our failure to pay an installment of interest (including additional amounts, if any) on any of the notes for 30 days after the date when due;

(3)

our failure to perform or observe any other covenant or agreement contained in the notes or the indenture for a period of 60 days after written notice of such failure, requiring us to remedy the same, shall have been given to us by the trustee or to us and the trustee by the holders of at least 25% in aggregate principal amount of the notes then outstanding;

(4)

a default under any indebtedness for money borrowed by us or any of our subsidiaries that is a "significant subsidiary" (as defined in Rule 405 of the Securities Act) the aggregate outstanding principal amount of which is in an amount in excess of $20 million, for a period of 30 days after written notice to us by the trustee or to us and the trustee by holders of at least 25% in aggregate principal amount of the notes then outstanding, which default:

•: is caused by a failure to pay principal or interest when due on such indebtedness by the end of the applicable grace period, if any, unless such indebtedness is discharged; or
•: results in the acceleration of such indebtedness, unless such acceleration is waived, cured, rescinded, annulled or such indebtedness is discharged; and

(5)

certain events of bankruptcy, insolvency or reorganization with respect to us or any of our subsidiaries that is a significant subsidiary.

The indenture provides that the trustee will, within 90 days of the occurrence of a default, give to the registered holders of the notes notice of all uncured defaults or events of default known to it, but the trustee shall be protected in withholding such notice if it, in good faith, determines that the withholding of such notice is in the best interest of such registered holders, except in the case of a default or event of default in the payment of the principal of or interest on, any of the notes when due or in the payment of any repurchase obligation.

If an event of default specified in clause (5) above occurs and is continuing with respect to us, then automatically the principal of all the notes and the interest thereon shall become immediately due and payable. If an event of default shall occur and be continuing, other than with respect to clause (5) above with respect to us (the default not having been cured or waived as provided under "—Modifications and Amendments" below), the trustee or the holders of at least 25% in aggregate principal amount of the notes then outstanding may declare the notes due and payable at their principal amount together with accrued interest, and thereupon the trustee may, at its discretion, proceed to protect and enforce the rights of the holders of notes by appropriate judicial proceedings. Such declaration may be rescinded or annulled with the written consent of the holders of a majority in aggregate principal amount of the notes then outstanding if all events of default (other than the nonpayment of amounts due solely as a result of such acceleration) have been cured or waived.

The indenture contains a provision entitling the trustee, subject to the duty of the trustee during default to act with the required standard of care, to be indemnified by the holders of notes before proceeding to exercise any right or power under the indenture at the request of such holders. The indenture provides that the holders of a majority in aggregate principal amount of the notes then outstanding may direct the time, method and place of conducting any proceeding for any remedy available to the trustee or exercising any trust or power conferred upon the trustee.

We will be required to furnish annually to the trustee a statement as to the fulfillment of our obligations under the indenture.

Modifications and Amendments

Changes Requiring Approval of Each Affected Holder

Except as set forth below and under "—Changes Requiring No Approval," we and the trustee may amend or supplement the indenture or the notes with the consent of the holders of a majority in aggregate principal amount of the outstanding notes. However, the indenture, including the terms and conditions of the notes, will not be able to be modified or amended without the written consent or the affirmative vote of the holder of each note affected by such change to:

•: change the maturity of the principal of or the date any installment of interest (including any payment of additional amounts) is due on any note;
•: reduce the principal amount or repurchase price of, or interest (including any payment of additional amounts) on, any note;
•: change the currency of payment of such note or interest thereon;
•: impair the right to institute suit for the enforcement of any payment on or on conversion of any note;
•: modify our obligations to maintain an office or agency in New York City;
•: except as otherwise permitted or contemplated by provisions concerning corporate reorganizations, adversely affect the repurchase rights of holders or the conversion rights of holders of the notes; or
•: reduce the percentage in aggregate principal amount of notes outstanding necessary to modify or amend the indenture or to waive any past default.

Changes Requiring No Approval

The indenture, including the terms and conditions of the notes, may be modified or amended by us and the trustee, without the consent of any holders of notes, for the purposes of, among other things:

•: adding to our covenants for the benefit of the holders of notes;
•: surrendering any right or power conferred upon us;
•: providing for conversion rights of holders of notes if any reclassification or change of our common stock or any consolidation, merger or sale of all or substantially all of our assets occurs;
•: providing for the assumption of our obligations to the holders of notes in the case of a merger, consolidation, conveyance, transfer or lease;
•: reducing the conversion price, provided that the reduction will not adversely affect the interests of the holders of notes;
•: complying with the requirements of the SEC in order to effect or maintain the qualification of the indenture under the Trust Indenture Act of 1939;
•: curing any ambiguity or correcting or supplementing any defective provision contained in the indenture, provided that such modification or amendment does not, in the good faith opinion of our board of directors, adversely affect the interests of the holders of notes in any material respect; or

•: adding or modifying any other provisions with respect to matters or questions arising under the indenture that we and the trustee may deem necessary or desirable and that will not, in the good faith opinion of our board of directors, adversely affect the interests of the holders of notes.

No Personal Liability of Directors, Officers, Employees or Stockholders

None of our directors, officers, employees or stockholders, as such, shall have any liability for any of our obligations under the notes or the indenture or for any claim based on, in respect of or by reason of such obligations or their creation. By accepting a note, each noteholder shall waive and release all such liability. The waiver and release shall be part of the consideration for the issue of the notes.

Governing Law

The indenture and the notes will be governed by, and construed in accordance with, the law of the State of New York.

Information Concerning the Trustee and the Transfer Agent

Wachovia Bank, National Association, as trustee under the indenture, has been appointed by us as paying agent, conversion agent, registrar and custodian with regard to the notes. StockTrans Inc. is the transfer agent and registrar for our common stock. The trustee or its affiliates may from time to time in the future provide banking and other services to us in the ordinary course of their business.

Registration Rights

Upon the closing of the notes offering, we entered into a registration rights agreement with the initial purchasers for the benefit of the holders of the notes. Pursuant to this agreement, we agreed, at our expense to, among other things, use our reasonable best efforts to keep the shelf registration statement effective until the earliest of:

•: two years after the last date of original issuance of any of the notes;
•: the date when the holders of the notes and the common stock issuable upon conversion of the notes are able to sell all such securities immediately without restriction pursuant to the volume limitation provisions of Rule 144 under the Securities Act; and
•: the date when all of the notes and the common stock into which the notes are convertible are registered under the shelf registration statement and disposed of in accordance with the shelf registration statement.

Each holder who sells securities pursuant to the shelf registration statement generally will be:

•: required to be named as a selling stockholder in the related prospectus;
•: required to deliver a prospectus to purchasers;
•: required to notify us of such sale within five business days after such sale;
•: subject to certain of the civil liability provisions under the Securities Act in connection with the holder's sales; and
•: bound by the provisions of the registration rights agreement which are applicable to the holder (including certain indemnification rights and obligations).

We may suspend the holder's use of the prospectus for a reasonable period not to exceed 45 days in any 90-day period, and not to exceed an aggregate of 90 days in any 360-day period, if:

•: the prospectus would, in our judgment, contain a material misstatement or omission as a result of an event that has occurred and is continuing; and
•: we reasonably determine that the disclosure of this material non-public information would have a material adverse effect on us and our subsidiaries taken as a whole.

However, if the disclosure relates to a previously undisclosed proposed or pending material business transaction, the disclosure of which would impede our ability to consummate such transaction, we may extend the suspension period from 45 days to 75 days. Each holder, by its acceptance of a note, agrees to hold any communication by us in response to a notice of a proposed sale in confidence.

If, after the effectiveness target date, the registration statement ceases to be effective or fails to be usable and (1) we do not cure the registration statement within five business days by a post-effective amendment or a report filed pursuant to the Exchange Act or (2) if applicable, we do not terminate the suspension period, described in the preceding paragraph, by the 45th or 75th day, as the case may be, or the suspension periods exceed an aggregate of 90 days in any 360 day period (each, a "registration default"), then in any such case additional amounts will be payable on the notes and the shares of common stock issued upon conversion of the notes that are Registrable Securities, from and including the day following the registration default to but excluding the day on which the registration default has been cured. Additional amounts will be paid semiannually in arrears, with the first semiannual payment due on the first interest payment date, as applicable, following the date on which such additional amounts begin to accrue, and will accrue at a rate per year equal to:

•: an additional 0.25% of the principal amount to and including the 90th day following such registration default; and
•: an additional 0.50% of the principal amount from and after the 91st day following such registration default.

In no event will additional amounts accrue at a rate per year exceeding 0.50%. If a holder has converted some or all of its notes into common stock, the holder will be entitled to receive equivalent amounts based on the principal amount of the notes converted.

If a shelf registration statement covering the resales of the notes and common stock into which the notes are convertible is not effective, these securities generally may not be sold or otherwise transferred except in accordance with exceptions under the Securities Act.

Rule 144A Information

We will furnish to the holders, beneficial holders and prospective purchasers of the notes and the common stock into which the notes are convertible, upon their request, the information required by Rule 144A(d)(4) under the Securities Act until such time as these securities are no longer "restricted securities" within the meaning of Rule 144 under the Securities Act, assuming these securities have not been owned by an affiliate of Primus.

Form, Denomination and Registration

Denomination and Registration

The notes will be issued in fully registered form, without coupons, in denominations of $1,000 principal amount and whole multiples of $1,000.

Global Notes; Book-Entry Form

Except as provided below, the notes will be evidenced by one or more global notes deposited with the trustee as custodian for DTC, and registered in the name of Cede & Co. as DTC's nominee.

Record ownership of the global notes may be transferred, in whole or in part, only to another nominee of DTC or to a successor of DTC or its nominee, except as set forth below. A holder may hold its interests in a global note directly through DTC if such holder is a participant in DTC, or indirectly through organizations which are direct DTC participants if such holder is not a participant in DTC. Transfers between direct DTC participants will be effected in the ordinary way in accordance with DTC's rules and procedures and will be settled in same-day funds. Holders may also beneficially own interests in the global notes held by DTC through certain banks, brokers, dealers, trust companies and other parties that clear through or maintain a custodial relationship with a direct DTC participant, either directly or indirectly. Transfers between direct DTC participants will be effected in the ordinary way in accordance with DTC's rules and procedures and will be settled in same-day funds.

So long as Cede & Co., as nominee of DTC, is the registered owner of the global notes, Cede & Co. for all purposes will be considered the sole holder of the global notes. Except as provided below, owners of beneficial interests in the global notes:

•: will not be entitled to have certificates registered in their names;
•: will not receive or be entitled to receive physical delivery of certificates in definitive form; and
•: will not be considered holders of the global notes.

The laws of some states require that certain persons take physical delivery of securities in definitive form. Consequently, the ability of an owner of a beneficial interest in a global note to transfer the beneficial interest in the global note to such persons may be limited.

We will wire, through the facilities of the trustee, payments of principal of and interest on the global notes to Cede & Co., the nominee of DTC, as the registered owner of the global notes. None of Primus, the trustee and any paying agent will have any responsibility or be liable for paying amounts due on the global notes to owners of beneficial interests in the global notes.

It is DTC's current practice, upon receipt of any payment of principal of and interest on the global notes, to credit participants' accounts on the payment date in amounts proportionate to their respective beneficial interests in the notes represented by the global notes, as shown on the records of DTC, unless DTC believes that it will not receive payment on the payment date. Payments by DTC participants to owners of beneficial interests in notes represented by the global notes held through DTC participants will be the responsibility of DTC participants, as is now the case with securities held for the accounts of customers registered in "street name."

If you would like to convert your notes into common stock pursuant to the terms of the notes, you should contact your broker or other direct or indirect DTC participant to obtain information on procedures, including proper forms and cut-off times, for submitting those requests.

Because DTC can only act on behalf of DTC participants, who in turn act on behalf of indirect DTC participants and other banks, your ability to pledge your interest in the notes represented by global notes to persons or entities that do not participate in the DTC system, or otherwise take actions in respect of such interest, may be affected by the lack of a physical certificate.

Neither Primus nor the trustee (nor any registrar, paying agent or conversion agent under the indenture) will have any responsibility for the performance by DTC or direct or indirect DTC participants of their obligations under the rules and procedures governing their operations. DTC has advised us that it will take any action permitted to be taken by a holder of notes, including, without limitation, the presentation of notes for conversion as described below, only at the direction of one or

more direct DTC participants to whose account with DTC interests in the global notes are credited and only for the principal amount of the notes for which directions have been given.

DTC has advised us as follows: DTC is a limited purpose trust company organized under the laws of the State of New York, a member of the Federal Reserve System, a "clearing corporation" within the meaning of the Uniform Commercial Code and a "clearing agency" registered pursuant to the provisions of Section 17A of the Securities Exchange Act. DTC was created to hold securities for DTC participants and to facilitate the clearance and settlement of securities transactions between DTC participants through electronic book-entry changes to the accounts of its participants, thereby eliminating the need for physical movement of certificates. Participants include securities brokers and dealers, banks, trust companies and clearing corporations and may include certain other organizations, such as the initial purchasers of the notes. Certain DTC participants or their representatives, together with other entities, own DTC. Indirect access to the DTC system is available to others such as banks, brokers, dealers and trust companies that clear through, or maintain a custodial relationship with, a participant, either directly or indirectly.

Although DTC has agreed to the foregoing procedures in order to facilitate transfers of interests in the global notes among DTC participants, it is under no obligation to perform or continue to perform such procedures, and such procedures may be discontinued at any time. If DTC is at any time unwilling or unable to continue as depositary and a successor depositary is not appointed by us within 90 days or an event of default has occurred and is continuing with respect to the notes, we will cause notes to be issued in definitive form in exchange for the global notes. None of Primus, the trustee or any of their respective agents will have any responsibility for the performance by DTC or direct or indirect DTC participants of their obligations under the rules and procedures governing their operations, including maintaining, supervising or reviewing the records relating to, or payments made on account of, beneficial ownership interests in global notes.

According to DTC, the foregoing information with respect to DTC has been provided to its participants and other members of the financial community for informational purposes only and is not intended to serve as a representation, warranty or contract modification of any kind.

DESCRIPTION OF CAPITAL STOCK

General

Our certificate of incorporation authorizes the issuance of 150,000,000 shares of common stock, and 2,455,000 shares of preferred stock, each par value $0.01 per share. As of September 30, 2003, our outstanding capital stock consisted of 65,521,195 shares of common stock held by 568 stockholders of record and 559,950 shares of Series C Preferred held of record by four stockholders. As of such date there were 13,333,587 shares of common stock reserved for issuance upon the exercise of stock options and other stock equivalents, 22,616,990 shares of common stock reserved for issuance pursuant to the conversion of the Series C Preferred, 14,157,925 shares of common stock reserved for issuance pursuant to the conversion of the notes offered under this prospectus, 1,428,342 shares of common stock reserved for issuance pursuant to the conversion of the 2007 Convertible Notes and 333,587 shares of common stock reserved for issuance pursuant to the exercise of the outstanding Warrants. The following summaries of certain provisions of our capital stock do not purport to be complete and are subject to, and qualified in their entirety by, the provisions of our certificate of incorporation and bylaws, which are available from us upon request, and by applicable law. We are a Delaware corporation and are subject to the Delaware General Corporation Law (DGCL).

Common Stock

Holders of common stock are entitled to one vote per share on all matters to be voted upon by our stockholders, and the holders of our common stock vote together as a single class on all matters to be voted upon by the stockholders. The holders of common stock are entitled to receive ratably dividends when, as and if declared from time to time by the board of directors out of our assets available for the payment of dividends to the extent permitted by law, subject to preferences that may be applicable to any outstanding preferred stock and any other provisions of our certificate of incorporation. We do not, however, anticipate paying any cash dividends in the foreseeable future.

Holders of common stock have no preemptive or other rights to subscribe for additional shares. No shares of common stock are subject to redemption or a sinking fund. Holders of common stock also do not have cumulative voting rights, which means the holder or holders of more than half of the shares voting for the election of directors can elect all the directors then being elected. In the event of any liquidation, dissolution or winding up of our company, whether voluntary or involuntary, after payment of our debts and other liabilities, and subject to the rights and liquidation preference, if any, of holders of shares of preferred stock, holders of common stock are entitled to share pro rata in any distribution of remaining assets to the stockholders. All of the outstanding shares of common stock are, and the shares issued upon conversion of the notes will be, fully paid and nonassessable.

Preferred Stock

We are authorized to issue up to 2,455,000 shares of preferred stock, par value $0.01 per share (the "Preferred Stock"), of which 455,000 shares are designated Series A Preferred Stock, 30,000 shares are designated Series B Junior Participating Preferred Stock, and 559,950 shares are designated Series C Preferred.

In addition to the Preferred Stock designated as described above, our board of directors, without further action by the holders of our common stock is also authorized to issue up to 1,410,050 shares of other Preferred Stock ("Other Preferred Stock"). Our board of directors may determine the timing, series, designation and number of shares of Other Preferred Stock to be issued, as well as the rights, preferences and limitations of such shares, including those related to voting power, redemption, conversion, dividend rights and liquidation preferences. The issuance of Other Preferred Stock would in certain circumstances be subject to the consent of the holders of the Series C Preferred, and could

adversely affect the voting power of the holders of our common stock or have the effect of deterring or delaying any attempt by a person, entity or group to obtain control of us.

Series C Preferred

Each share of Series C Preferred was initially convertible into common stock at a rate of forty (40) shares of common stock for each share of Series C Preferred (the "Conversion Ratio") resulting in an effective conversion price per share of common stock (the "Effective Conversion Price") of $1.875. The Conversion Ratio and the Effective Conversion Price are subject in each case from time-to-time to weighted-average anti-dilution adjustments, provided that such adjustments do not result in an adjusted Effective Conversion Price per share of common stock of less than $1.754 per share. The Effective Conversion Price as of September 30, 2003 for the Series C Preferred was $1.857 per share and the Conversion Ratio as of such date was 40.3911 shares of common stock for each share of Series C Preferred. These prices and ratios were adjusted following the initial closing for the Series C Preferred on December 31, 2002 (the "Initial Closing") due to the operation of performance adjustment provisions that were in effect as of December 31, 2002 and which were extinguished as of February 13, 2003, upon Primus's satisfaction of related performance milestone provisions under the Series C Preferred terms.

Each Series C Preferred share is convertible into common stock at any time. All shares are mandatorily convertible if (i) two-thirds of the holders elect to convert or (ii) the average closing price of our common stock for any period of 20 consecutive trading days exceeds three times the then Effective Conversion Price, and all of the then outstanding shares of Series C Preferred are no longer subject to transfer restrictions as contained in, and may be sold or transferred by such Series C Preferred holders in compliance with, Rule 144(k) and Rule 145 under the Securities Act of 1933, as amended.

The holders of Series C Preferred are entitled to receive non-cumulative dividends in preference to any dividend on the common stock, when, as and if declared by our board of directors, at the rate of 8% of the per share purchase price of the Series C Preferred per annum. Any such dividends declared by the Board may be paid at the discretion of the Board in cash, in shares of our common stock or by any combination of cash or shares. Common stock paid as a dividend will be valued at the average daily closing price of our common stock during the consecutive 30-day trading period ending on the applicable dividend date. Each share of Series C Preferred is entitled to a liquidation preference payment ahead of the common stock equal to the then applicable Effective Conversion Price multiplied by the number of shares of common stock into which such share is convertible plus an amount representing a 15% internal rate of return (less dividends, distributions and performance adjustment payments previously made) on the allocable purchase price paid to us for such share.

Board Representation

For so long as the issued and outstanding shares of Series C Preferred (together with all common stock owned by holders of Series C Preferred) represent at least ten percent (10%) of the total outstanding voting power of the Company on a "Fully Diluted Basis" (as defined below), the holders of Series C Preferred shall be entitled to elect, by majority vote of the Series C Preferred, one member of the board of directors (the "Preferred Director") and one non-voting observer to the board of directors (the "Board Observer"); provided that the Preferred Director and the Board Observer are reasonably acceptable to a majority of the other directors of the Company (it being agreed that Paul G. Pizzani is acceptable as the Preferred Director and Geoffrey L. Hamlin is acceptable as the Board Observer). Following the Initial Closing, the holders of Series C Preferred exercised the foregoing rights and elected Paul G. Pizzani as the Preferred Director and Geoffrey L. Hamlin as the Board Observer. In the event that the outstanding shares of Series C Preferred represent less than ten percent (10%) of the outstanding voting power but more than five percent (5%) of the total outstanding voting power of

the Company on a Fully Diluted Basis (this time excluding any Common Stock owned by holders of Series C Preferred), the holders of Series C Preferred shall be entitled to elect a Preferred Director but no Board Observer. For purposes of determining a stockholder's ownership percentage for the taking of an action in accordance with the Series C Preferred terms, "Fully Diluted Basis" shall mean the inclusion of all issued and outstanding shares of common stock plus the maximum number of shares of common stock issuable upon the exercise or conversion of all outstanding debt and equity securities (including, without limitation, shares of Series C Preferred, warrants and options to purchase capital stock of Primus).

In the event a Board Observer is elected by the holders of Series C Preferred, such individual shall be entitled to attend meetings of the Company's Board of Directors in a non-voting capacity. The Board Observer shall be entitled to receive all materials distributed to the Board of Directors but shall be subject to the same obligations as directors with respect to confidentiality, conflicts of interest and misappropriation of corporate opportunities, shall not be entitled to vote on, engage in discussion of or otherwise participate in any matter submitted to the Board of Directors and shall be subject to exclusion from meetings or portions thereof for purposes of protecting the attorney-client privilege or other confidential information.

Protective Provisions

For so long as the outstanding Series C Preferred represents ten percent (10%) or more of the total outstanding voting power of Primus on a Fully Diluted Basis, Primus may not without the approval of a majority of the issued and outstanding Series C Preferred, voting separately as a class:

•: authorize or issue equity securities or rights to purchase or acquire equity securities with rights to dividends or liquidation preference that are senior to or pari passu with the Series C Preferred; or
•: amend or waive provisions of our organizational documents in a manner material and adverse to rights of the Series C Preferred.

For so long as the outstanding Series C Preferred represents ten percent (10%) or more of the total outstanding voting power of Primus on a Fully Diluted Basis, Primus may not without majority approval by the Preferred Director and the other non-management directors of Primus, voting together as a group:

•: merge or consolidate Primus or any subsidiary with annual revenues of at least $75,000,000 (a "Material Subsidiary") unless there is no change of control of Primus or any Material Subsidiary, measured by majority equity ownership;
•: sell, transfer or dispose of all or substantially all of the assets of Primus or any Material Subsidiary;
•: incur indebtedness in excess of $535 million of Net Debt (defined below);
•: redeem, repurchase, or reacquire senior or pari passu debt or equity (other than debt or equity issued and outstanding as of the Initial Closing for the Series C Preferred or equity issued after the Initial Closing that is approved consistent with the Series C Preferred terms);
•: authorize total common stock issuable upon the exercise of employee, consultant and certain other options (whether granted prior to, on or after the second closing of the Series C Preferred on April 3, 2003) in excess of 9,000,000 shares (subject to replenishment upon the forfeiture of unvested options);
•: liquidate, reorganize, recapitalize, declare bankruptcy, consent to a receiver, or effect a general assignment for the benefit of creditors; or

•: issue common stock or common stock equivalents at an effective purchase price per share (including the assumed payment of all applicable exercise or conversion payments at the time of issuance) that is less than the average closing price of the common stock for the consecutive 20-day trading period preceding such issuance, other than certain excluded issuances.

"Net Debt" means indebtedness of Primus with a maturity of one (1) year or more (excluding any such indebtedness incurred by Primus in connection with its acquisition of assets pursuant to that certain Customer Transfer Agreement by and between Primus and C&W dated September 13, 2002) less our unrestricted cash balance (including proceeds from the Initial Closing and Second Closing not used to achieve certain leverage criteria described in the Purchase Agreement) as of the last day of the quarter preceding the calculation date.

Common Stock Warrants

As of September 30, 2003, we had outstanding warrants for the purchase of 333,587 shares of common stock at an exercise price of $9.075 per share.

The exercise price of the warrants is subject to adjustment upon the occurrence of certain events, including, among other things, the payment of a stock dividend, a merger or consolidation and the issuance for consideration of rights, options or warrants (other than rights to purchase common stock issued to stockholders generally) to acquire our common stock. A holder of any of the warrants described above will not be entitled to any rights as a stockholder of us, including, without limitation, the right to vote with respect to the shares of our common stock, until such holder has exercised the warrants.

Registration Rights

Holders of Series C Preferred. Simultaneously with the initial closing of the sale of the Series C Preferred, we entered into a registration rights agreement, pursuant to which we granted to the purchasers of the Series C Preferred (and their affiliates and permitted transferees) (the "Designated Holders") registration rights with respect to the shares of common stock issuable upon conversion of the Series C Preferred held by the Designated Holders (collectively, the "Series C Registrable Securities").

At any time after the date of the registration rights agreement, the Designated Holders holding at least two-thirds of the Series C Registrable Securities may cause us to file a registration statement under the Securities Act, with respect to their Series C Registrable Securities, so long as the aggregate proceeds to them from the registration statement is expected to exceed $10.0 million (a "Demand Registration"). The Designated Holders are entitled to two Demand Registrations, but in the case of an underwritten Demand Registration, if the number of Series C Registrable Securities to be registered on any particular registration statement is reduced to less than 67% of the Series C Registrable Securities initially requested to be registered, the Designated Holders will be entitled to one additional Demand Registration. Designated Holders whose shares are not included in the initial request for registration may also register their Series C Registrable Securities in the Demand Registration.

The Designated Holders also have unlimited piggyback registrations, as well as the right to request registrations of their Series C Registrable Securities on Form S-3, subject to certain limitations, so long as the aggregate proceeds to them from a particular Registration Statement is expected to exceed $1.0 million (an "S-3 Registration").

We may postpone the filing of a registration statement relating to a Demand Registration or an S-3 Registration for certain specified valid business reasons described in the registration rights agreement, but in no event for more than 150 days, and we may withdraw a filed registration statement in the event of any valid business reason not resulting from our actions. We may exercise this right to

postponement or withdrawal no more than once in any 12-month period. For so long as the purchasers of Series C Preferred (and their affiliates and permitted transferees) hold at least 10% of the outstanding voting power of our stockholders on an as-converted to common stock and fully diluted basis, we may not grant additional registration rights to any party without the prior consent of a majority of our non-employee directors, unless such registration rights are subordinate to the rights granted under the registration rights agreement.

All such registrations would be at our expense, exclusive of underwriting discounts and commissions. We and the holders of the Series C Preferred have entered into customary indemnification and contribution provisions.

Takeover Protections

Classified Board

Pursuant to our Certificate of Incorporation, our board of directors is divided into three classes of directors each containing, as nearly as possible, an equal number of directors. Directors within each class are elected to serve three-year terms and approximately one-third of the directors sit for election at each annual meeting of our stockholders; provided, that the Series C Director is elected by the holders of Series C Preferred as a class, not by all stockholders of Primus. A classified board of directors may have the effect of deterring or delaying any attempt by any group to obtain control of Primus by a proxy contest since such third party would be required to have its nominees elected at two separate annual meetings of our stockholders in order to elect a majority of the members of the board of directors. Directors who are elected to fill a vacancy (including vacancies created by an increase in the number of directors) must be confirmed by the stockholders at the next annual meeting of stockholders whether or not such director's term expires at such annual meeting.

Other Protections Under By-Laws

Our by-laws allow the board of directors to increase the number of directors from time to time and to fill any vacancies on the board of directors, including vacancies resulting from an increase in the number of directors. This provision is designed to provide the board of directors with flexibility to deal with an attempted hostile takeover by a stockholder who may acquire a majority voting interest in us without paying a premium. This provision allows the board of directors to increase its size and prevent a "squeeze-out" of any remaining minority interest soon after a new majority stockholder gains control over us. Further, the by-laws limit the new majority stockholder's power to remove a current or all current directors before the annual meeting in the absence of "cause." Cause for removal of a director is limited to:

•: a judicial determination that a director is of unsound mind;
•: a conviction of a director of an offense punishable by imprisonment for a term of more than one year;
•: a breach or failure by a director to perform the statutory duties of said director's office if the breach or failure constitutes self-dealing, willful misconduct or recklessness; or
•: a failure of a director, within 60 days after notice of his or her election, to accept such office either in writing or by attending a meeting of the board of directors and fulfilling such other requirements of qualification as the by-laws or certificate of incorporation may provide.

Rights Agreement

We are party to an agreement with StockTrans, Inc., as Rights Agent, dated December 23, 1998 (as amended, the "Rights Agreement"). The Rights Agreement provides for the distribution of rights that

entitle the registered holder, subject to the terms of the Rights Agreement (including the Exchange Right described in the succeeding paragraph), to purchase from us one-thousandth of a share (a "Unit") of Series B Junior Participating Preferred Stock, par value $0.01 per share (the "Series B Preferred"), at a purchase price of $90.00 per Unit, subject to adjustment (the "Rights"). Each Unit is designed to be the economic equivalent of one share of our common stock. The Rights are presently attached to all certificates representing shares of outstanding common stock and generally will attach to shares of common stock issuable in the future upon conversion of Series C Preferred. The Rights will separate from the common stock and the Rights will become exercisable (such date, a "Distribution Date") upon the earlier of:

•: ten business days following a public announcement (the date of such announcement being the "Stock Acquisition Date") that a person or group of affiliated or associated persons (an "Acquiring Person") has acquired, obtained the right to acquire, or otherwise obtained beneficial ownership of 20% or more of the then outstanding shares of common stock; or
•: ten business days following the commencement of a tender offer or exchange offer that would result in an Acquiring Person owning 20% or more of the then outstanding shares of common stock, or such later date as may be determined by action of a majority of the members of the board of directors (such determination to be made prior to such time as any person becomes an Acquiring Person).

The term "Acquiring Person" does not include us, any of our subsidiaries, any of our employee benefit plans or employee stock plans, or any holder of our Series C Preferred (or the common stock issuable upon conversion of the Series C Preferred) (each such person or entity being referred to as an "Exempt Person").

In the event that

•: we are the surviving corporation in a merger with an Acquiring Person and shares of common stock shall remain outstanding;
•: a person or group of affiliated or associated persons becomes the beneficial owner of 20% or more of the then outstanding shares of common stock;
•: an Acquiring Person engages in one or more "self-dealing" transactions as set forth in the Rights Agreement; or
•: during such time as there is an Acquiring Person, an event occurs which results in such Acquiring Person's ownership interest being increased by more than 1% (e.g., by means of a reverse stock split or recapitalization);

then, in each case, each holder of a Right will thereafter have the right to receive, upon exercise, a Unit of Series B Preferred (or, in certain circumstances, common stock, cash, property or other of our securities) having a value equal to two times the exercise price of the Right. The exercise price is the purchase price multiplied by the number of Units of Series B Preferred issuable upon exercise of a Right prior to the events described in this paragraph. Our board of directors may, at its option, at any time after a person becomes an Acquiring Person, cause us to exchange all or any part of the then outstanding and exercisable Rights for shares of our common stock at an exchange ratio of one share per Right (as adjusted for stock splits, stock dividends or similar transactions) or for Units of our Preferred Stock designed to have the same voting rights as one share of our common stock (the "Exchange Right"). The Exchange Right will terminate once any person (other than an Exempt Person), together with that person's affiliates and associates, becomes the beneficial owner of a majority of our common stock then outstanding. Notwithstanding any of the foregoing, following the occurrence of any of the events set forth in this paragraph, all Rights that are, or (under certain circumstances

specified in the Rights Agreement) were, beneficially owned by any Acquiring Person will be null and void.

In the event that, at any time following the Stock Acquisition Date,

•: we are acquired in a merger or other business combination transaction and we are not the surviving corporation (other than a merger described in the preceding paragraph);
•: any person or group of affiliated or associated persons consolidates or merges with us and all or part of the common stock is converted or exchanged for securities, cash or property of any other person or group of affiliated or associated persons; or
•: 50% or more of our assets or earning power is sold or transferred,

each holder of a Right (except the Rights which previously have been voided or exchanged as described above) shall thereafter have the right to receive, upon exercise, common stock of the Acquiring Person having a value equal to two times the exercise price of the Right.

The Rights are not exercisable until the Distribution Date and will expire on December 23, 2008 unless the term of the agreement is extended or the Rights are earlier redeemed or exchanged by us. At the time until ten business days following the Stock Acquisition Date or such later date as a majority of the members of the board of directors shall determine (such determination to be made prior to the date specified by the Rights Agreement), a majority of the board of directors may redeem the Rights in whole, but not in part, at a price of $0.001 per Right (subject to adjustment in certain events) (the "Redemption Price"). Immediately upon the action of a majority of the board of directors ordering the redemption of the Rights, the Rights will terminate and the only right of the holders of Rights will be to receive the Redemption Price.

Statutory Provisions

We are subject to Section 203 of the DGCL which, subject to certain exceptions, prohibits a Delaware corporation, the voting stock of which is generally publicly traded (i.e., listed on a national securities exchange or authorized for quotation on an inter-dealer quotation system of a registered national securities association) or held of record by more than 2,000 stockholders, from engaging in any "business combination" (as defined below) with any "interested stockholder" (as defined below) for a period of three years following the date that such stockholder became an interested stockholder, unless:

•: prior to such date, the board of directors of the corporation approved either the business combination or the transaction which resulted in the stockholder becoming an interested stockholder;
•: upon consummation of the transaction which resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction commenced, excluding for purposes of determining the number of shares outstanding those shares owned (1) by persons who are directors and also officers, and (2) by employee stock plans in which employee participants do not have the right to determine confidentially whether shares held subject to the plan will be tendered in a tender or exchange offer; or
•: on or subsequent to such date, the business combination is approved by the board of directors and authorized at an annual or special meeting of stockholders, and not by written consent, by the affirmative vote of at least 66²/3% of the outstanding voting stock which is not owned by the interested stockholder.
•: Section 203 of the DGCL defines "business combination" to include:
•: any merger or consolidation involving the corporation and the interested stockholder;

•: any sale, transfer, pledge or other disposition involving the interested stockholder of 10% or more of the assets of the corporation;
•: subject to certain exceptions, any transaction which results in the issuance or transfer by the corporation of any stock of the corporation to the interested stockholder;
•: any transaction involving the corporation which has the effect of increasing the proportionate share of the stock of any class or series of the corporation beneficially owned by the interested stockholder; or
•: the receipt by the interested stockholder of benefits provided by or through the corporation. In general, Section 203 defines an "interested stockholder" as any person who, together with any affiliates or associates of such person, beneficially owns, directly or indirectly, 15% or more of the outstanding voting stock of a Delaware corporation.

This provision of the DGCL could prohibit or delay mergers or other takeover or change of control attempts with respect to us and, accordingly, may discourage attempts that might result in a premium over the market price for shares held by our stockholders.

Acceleration of Vesting

Upon a change of control, our board of directors may accelerate the vesting of all unvested options issued pursuant to our stock option plans. The acceleration of vesting of such options upon a change of control may have the effect of discouraging a third party from making a tender offer or otherwise attempting to obtain control of us by making any such transaction more costly.

Repurchase of Senior Notes

Upon a change of control, pursuant to the indentures governing each of our senior notes (other than the 1997 senior notes), the holders of such senior notes may require us to repurchase their senior notes at 101% of principal plus accrued interest. A similar provision is contained in the indenture governing our 2000 convertible debentures and the indenture governing the notes offered hereby. These provisions may have the effect of discouraging a third party from making a tender offer or otherwise attempting to obtain control of us.

Indemnification of Directors and Officers

Section 145 of the DGCL provides the power to indemnify any director or officer acting in his capacity as our representative who was, is or is threatened to be made a party to any action or proceeding for expenses, judgments, penalties, fines and amounts paid in settlement in connection with that action or proceeding. The indemnity provisions apply whether the action was instituted by a third party or arose by or in our right. Generally the only limitations on our ability to indemnify our director or officer is that the director or officer acted in good faith in a manner reasonably believed to be in, or not opposed to, the best interests of the corporation and, with respect to any criminal action, that the director or officer has no reasonable cause to believe that his conduct was unlawful.

Article V of our by-laws provides that we will indemnify any person by reason of the fact that he or she is or was a director, officer, employee or agent of Primus (or is or was serving in such capacity for another entity at our request). To the extent that a director, officer, employee or agent of ours has been successful on the merits or otherwise in defense of any action, suit or proceeding referred to in such Article V, or in defense of any claim, issue or matter therein, he or shall be indemnified by us against actually and reasonably incurred expenses in connection therewith. Such expenses may be paid by us in advance of the final disposition of the action upon receipt of an undertaking to repay the advance if it is ultimately determined that such person is not entitled to indemnification.

Our by-laws authorize us to take steps to ensure that all persons entitled to indemnification are properly indemnified, including, if the board of directors so determines, purchasing and maintaining insurance. We have obtained a policy insuring our directors and officers against certain liabilities, including liabilities under the Securities Act.

Limitation of Liability

Our certificate of incorporation provides that none of our directors shall be personally liable to us or our stockholders for monetary damages for a breach of fiduciary duty as a director, except for liability:

•: for any breach of that person's duty of loyalty to us or our stockholders;
•: for acts or omissions not in good faith or involving intentional misconduct or a knowing violation of law;
•: for the unlawful payment of dividends on or redemption of our capital stock; and
•: for any transaction from which that person derived an improper personal benefit.

We maintain directors and officers' liability insurance to provide directors and officers with insurance coverage for losses arising from claims based on breaches of duty, negligence, error and other wrongful acts. At present, except for the litigation described in this prospectus, there is no pending litigation or proceeding, and we are not aware of any threatened litigation or proceeding, involving any director or officer where indemnification will be required or permitted under our certificate of incorporation or our by-laws.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is StockTrans, Inc.

MATERIAL UNITED STATES FEDERAL INCOME TAX CONSEQUENCES

The following is a discussion of the material United States federal income tax consequences of the ownership of the notes and shares of common stock issued upon conversion of the notes ("conversion shares") as of the date hereof. Except where noted, this summary deals only with notes and conversion shares held as capital assets and does not deal with special situations. For example, this summary does not address:

•: tax consequences to holders who may be subject to special tax treatment, such as dealers in securities or currencies, financial institutions, tax-exempt entities, traders in securities that elect to use a mark-to-market method of accounting for their securities holdings, corporations that accumulate earnings to avoid federal income tax or life insurance companies;
•: tax consequences to persons holding notes or conversion shares as part of a hedging, integrated, constructive sale or conversion transaction or a straddle;
•: tax consequences to holders of notes or conversion shares whose "functional currency" is not the USD;
•: AMT consequences, if any; or
•: any state, local or foreign tax consequences.

The discussion below is based upon the provisions of the Internal Revenue Code of 1986, as amended (the "Code"), and regulations, rulings and judicial decisions as of the date hereof. Those authorities may be changed, perhaps retroactively, so as to result in United States federal income tax consequences different from those discussed below.

If you are considering the purchase of notes, you should consult your own tax advisors concerning the United States federal income tax consequences to you and any consequences arising under the laws of any other taxing jurisdiction.

Consequences to United States Holders

The following is a summary of the United States federal tax consequences that will apply to you if you are a United States holder of notes or conversion shares.

The material consequences to "Non-United States Holders" of notes and conversion shares are described under "Consequences to Non-United States Holders" below. "United States Holder" means a beneficial owner of a note that is:

•: a citizen or resident of the United States or someone treated as a citizen or resident of the United States for United States federal income tax purposes;
•: a corporation (or any entity treated as a corporation for United States federal income tax purposes) created or organized in or under the laws of the United States or any political subdivision of the United States;
•: an estate the income of which is subject to United States federal income taxation regardless of its source; or
•: a trust that (1) is subject to the supervision of a court within the United States and the control of one or more United States persons or (2) has a valid election in effect under applicable United States Treasury regulations to be treated as a United States person.

Payment of Interest

United States Holders will be required to recognize as ordinary income any interest paid or accrued on the notes in accordance with their regular method of accounting.

We are obligated to pay additional amounts to holders of the notes and conversion shares that are Registrable Securities as described in "Description of the Notes—Registration Rights." Any payments of additional amounts should be taxable as ordinary income in accordance with the holder's regular method of accounting.

Constructive Dividend

The conversion price of the notes will be adjusted in certain circumstances. Under Section 305(c) of the Code, adjustments (or failures to make adjustments) that have the effect of increasing your proportionate interest in our assets or earnings may in some circumstances result in a deemed distribution to you. Any deemed distributions will be taxable as a dividend, return of capital or capital gain in accordance with the earnings and profits rules under the Code.

Generally, a reasonable increase in the conversion rate in the event of stock dividends or distributions of rights to subscribe for our common stock will not be a taxable dividend. Certain adjustments provided in the notes (including, without limitation, adjustments in respect of taxable dividends to our stockholders) will not qualify as being pursuant to a bona-fide reasonable formula. If such an adjustment is made, you will be deemed to have received a constructive distribution taxable as a dividend to the extent of our current or accumulated earnings and profits even though you have not received any cash or property as a result of the adjustment. It is not clear whether a constructive dividend deemed paid to you would be eligible for the preferential rates of United States federal income tax applicable to certain dividends under recently enacted legislation. It is also unclear whether corporate holders would be entitled to claim the dividends received deduction with respect to any such constructive dividends.

Sale, Exchange and Retirement of Notes

Except as provided below under "—Conversion of Notes into Common Shares," you will generally recognize gain or loss upon the sale, exchange, retirement or other disposition of a note equal to the difference between the amount realized (less any accrued interest which will be taxable as such) upon the sale, exchange, retirement or other disposition and your adjusted tax basis in the note. Your tax basis in a note will generally be equal to the amount you paid for the note. Any gain or loss will be capital gain or loss. If you are an individual and have held the note for more than one year, your capital gain may be taxable at a reduced rate. Your ability to deduct capital losses may be limited.

If, upon a change in control, you require us to repurchase some or all of your notes and we elect to pay the repurchase price in shares of our common stock or in a combination of shares of our common stock and cash, the redemption would likely qualify as a recapitalization for United States federal income tax purposes if the notes qualify as "securities" for those purposes. Whether the notes qualify as "securities" is not free from doubt. Please consult your own tax advisor regarding such determination. If the redemption qualifies as a recapitalization, you would not recognize any income, gain or loss on your receipt of our common stock in exchange for notes (except to the extent of cash received, if any, including cash received in lieu of fractional shares and except to the extent of amounts received attributable to accrued interest, which would be taxable as such). If a combination of cash and stock is received in exchange for your notes, the amount of gain recognized would be equal to the excess of the fair market value of the common stock and cash received over your adjusted tax basis in the note, but in no event should the amount recognized exceed the amount of cash received. If you receive cash in lieu of fractional shares of stock, you would be treated as if you received the fractional share and then had the fractional share redeemed for cash. You would recognize gain or loss equal to

the difference between the cash received and that portion of your basis in the stock attributable to the fractional share. Your aggregate basis in the stock would equal your adjusted basis in the note (excluding the portion of the tax basis that is allocable to any fractional share for which cash is paid), reduced by the amount of any cash received (other than cash received in lieu of a fractional share) and increased by the amount of gain, if any, recognized (other than with respect to a fractional share). Your holding period for the stock would include the period during which you held the note. If the redemption does not qualify as a recapitalization, you may recognize income, gain or loss on your receipt of our common stock in exchange for notes.

Conversion of Notes into Common Shares

You will not recognize gain or loss on the conversion of your notes into conversion shares (except to the extent of cash received in lieu of a fractional conversion share). The amount of gain or loss on the deemed sale of such fractional conversion share will be equal to the difference between the amount of cash you receive in respect of such fractional conversion share and the portion of your tax basis in the note that is allocable to the fractional conversion share. The tax basis of the conversion shares received upon a conversion will equal the adjusted tax basis of the note that was converted, reduced by the portion of the tax basis that is allocable to any fractional conversion share. Your holding period for conversion shares will include the period during which you held the notes.

Dividends

If, after you exchange a note for our common stock we make a distribution of cash or other property (other than certain pro rata distributions of our common stock) in respect of that stock, the distribution will be treated as a dividend to the extent that it is paid from our current or accumulated earnings or profits. If you are a noncorporate United States Holder, including an individual, and provided you hold the common stock for more than 60 days during the 120-day period beginning 60 days before the ex-dividend date, such dividend will be taxable to you at a maximum rate of 15% (through December 31, 2008 after which time it will revert to being taxable at ordinary income rates). If the distribution exceeds current or accumulated earnings and profits, the excess will be treated first as a tax-free return of your investment to the extent of your basis in such common stock. Any amounts in excess of such basis will be treated as capital gain. If you are a corporation, you may be able to claim a deduction for a portion of any distribution received that is considered a dividend.

Sale or Other Disposition of Common Stock

You will generally recognize capital gain or loss on a sale or other disposition of our common stock. Your gain or loss will equal the difference between the proceeds you receive and your adjusted tax basis in the stock. The proceeds received will include the amount of any cash and the fair market value of any other property received for the stock. If you are a noncorporate United States Holder, including an individual, and have held the stock for more than one year, such capital gain will be subject to tax at a maximum rate of 15% (through December 31, 2008, after which time it will revert to a maximum rate of 20%). Your ability to deduct capital losses may be limited.

Information Reporting and Backup Withholding

In general, information reporting requirements will apply to certain payments of principal and interest paid on the notes and dividends paid on the conversion shares and to the proceeds of sale of a note or conversion share made to you unless you are an exempt recipient (such as a corporation). A 28 percent backup withholding tax will apply to such payments if you fail to provide your taxpayer identification number or certification of foreign or other exempt status or fail to report in full dividend and interest income.

Any amounts withheld under the backup withholding rules will be allowed as a refund or a credit against your United States federal income tax liability provided the required information is furnished to the Internal Revenue Service (the "IRS").

Consequences to Non-United States Holders

The following is a summary of the United States federal tax consequences that will apply to you if you are a Non-United States Holder of notes or conversion shares. The term "Non-United States Holder" means a beneficial owner of a note that is not a United States Holder.

United States Federal Withholding Tax

The 30% United States federal withholding tax will not apply to any payment to you of principal or interest on a note provided that:

•: interest paid on the note is not effectively connected with your conduct of a trade or business in the United States;
•: you do not actually or constructively own 10% or more of the total combined voting power of all classes of our stock that are entitled to vote within the meaning of section 871(h)(3) of the Code;
•: you are not a controlled foreign corporation that is related to us through stock ownership within the meaning of Section 864(d)(4) of the Code;
•: you are not a bank whose receipt of interest on a note is described in section 881(c)(3)(A) of the Code; and
•: you provide your name and address, and certify, under penalties of perjury, that you are not a United States person (which certification may be made on an IRS Form W-8BEN (or successor form)) or a financial institution holding the note on your behalf certifies, under penalties of perjury, that such statement has been received by it and furnishes a paying agent with a copy thereof.

If you cannot satisfy the requirements described above, payments of interest will be subject to the 30% United States federal withholding tax, unless you provide us with a properly executed (1) IRS Form W-8BEN (or successor form) claiming an exemption from or reduction in withholding under the benefit of a tax treaty or (2) IRS Form W-8ECI (or successor form) stating that interest paid on the note is not subject to withholding tax because it is effectively connected with your conduct of a trade or business in the United States.

Any dividends paid to you with respect to the conversion shares (and any deemed dividends resulting from certain adjustments, or failure to make adjustments, to the number of shares issued on conversion (see "—Constructive Dividend" above)) generally will be subject to withholding tax at a 30% rate or such lower rate as may be specified by an applicable income tax treaty. However, dividends that are effectively connected with the conduct of a trade or business within the United States and, where a tax treaty applies, are attributable to a United States permanent establishment, are not subject to the withholding tax, but instead are subject to United States federal income tax on a net income basis at applicable graduated individual or corporate rates. In order to be exempt from withholding tax under this exception, you must provide us with a properly executed IRS Form W-8ECI (or successor form) stating that dividends paid on the conversion shares are not subject to withholding tax because the conversion shares are effectively connected with your conduct of a trade or business in the United States. If you are a foreign corporation, any such effectively connected dividends may, under certain circumstances, be subject to an additional "branch profits tax" at a 30% rate or such lower rate as may be specified by an applicable income tax treaty.

The 30% U.S. federal withholding tax will not apply to any gain that you realize on the sale, exchange, retirement or other disposition of a note or conversion share.

United States Federal Estate Tax

The United States federal estate tax will not apply to notes owned by you at the time of your death, provided that any payment to you on the notes would be eligible for exemption from the 30% United States federal withholding tax under the rules described above under "—United States Federal Withholding Tax" without regard to the statement requirement described in the last bullet point. However, conversion shares held by you at the time of your death will be included in your gross estate for United States federal estate tax purposes unless an applicable estate tax treaty provides otherwise.

United States Federal Income Tax

If you are engaged in a trade or business in the United States and interest on a note or dividends on a conversion share are effectively connected with the conduct of that trade or business, you (although exempt from the 30% withholding tax) will be subject to United States federal income tax on that interest or dividend on a net income basis in the same manner as if you were a United States person as defined under the Code. In addition, if you are a foreign corporation, you may be subject to a branch profits tax equal to 30% (or lower applicable treaty rate) of your earnings and profits for the taxable year, subject to adjustments, that are effectively connected with your conduct of a trade or business in the United States. For this purpose, interest and dividends on the conversion shares will be included in earnings and profits.

Any gain or income realized on the disposition of a note or conversion share generally will not be subject to United States federal income tax unless (1) that gain or income is effectively connected with the conduct of a trade or business in the United States by you, (2) you are an individual who is present in the United States for 183 days or more in the taxable year of that disposition, and certain other conditions are met or (3) we are or have been a "United States real property holding corporation" for United States federal income tax purposes.

We believe that we are not and we do not anticipate becoming a United States real property holding corporation.

Information Reporting and Backup Withholding

Generally, we must report to the IRS and to you the amount of interest and dividends paid to you and the amount of tax, if any, withheld with respect to these payments. Copies of the information returns reporting such interest and dividend payments and any withholding may also be made available to the tax authorities in the country in which you reside under the provisions of an applicable income tax treaty.

In general, you will not be subject to backup withholding with respect to payments that we make to you provided that we do not have actual knowledge or reason to know that you are a United States person and you have given us the statement described above under "—United States Federal Withholding Tax."

In addition, you will not be subject to backup withholding or information reporting with respect to the proceeds of the sale of a note or conversion share within the United States or conducted through certain United States-related financial intermediaries, if the payer receives the statement described above and does not have actual knowledge or reason to know that you are a United States person, as defined under the Code, or you otherwise establish an exemption.

The preceding discussion of certain U.S. federal income tax consequences is for general information only. It is not tax advice. Each prospective investor should consult its own tax advisor regarding the particular U.S. federal, state, local, and foreign tax consequences of purchasing, holding, and disposing of our notes or common stock, including the consequences of any proposed change in applicable laws.

SELLING SECURITY HOLDERS

We originally issued and sold the notes to the initial purchasers in transactions exempt from the registration requirements of the Securities Act, and the initial purchasers immediately resold the notes to persons they reasonably believed to be qualified institutional buyers. Selling holders, including their transferees, pledgees or donees or their successors, may from time to time offer and sell pursuant to this prospectus any or all of the notes and common stock into which the notes are convertible.

The following table sets forth information with respect to the selling holders and the principal amounts of notes beneficially owned by each selling holder that may be offered under this prospectus. The information is based on information provided by or on behalf of the selling holders. The selling holders may offer all, some or none of the notes or common stock into which the notes are convertible. Because the selling holders may offer all or some portion of the notes or the common stock, no estimate can be given as to the amount of the notes or the common stock that will be held by the selling holders upon termination of any sales: the table below assumes that all selling holders will sell all of their notes or common stock, unless otherwise indicated. In addition, the selling holders identified below may have sold, transferred or otherwise disposed of all or a portion of their notes or common stock since the date on which the information was provided regarding their notes and common stock in transactions exempt from the registration requirements of the Securities Act.

Name	Principal Amount of Notes Beneficially Owned and Offered(1)	Principal Amount of Notes Owned After Completion of Offering	Common Stock Beneficially Owned After Completion of the Offering
Wyoming State Treasurer	740,000	-0-	-0-
San Diego City Retirement	675,000	-0-	-0-
Arkansas Teachers Retirement	3,345,000	-0-	-0-
San Diego County Convertible	1,440,000	-0-	-0-
Engineers Joint Pension Fund	315,000	-0-	-0-
Wake Forest University	440,000	-0-	-0-
Nicholas Applegate Capital Mgmt. Cont. Fund	575,000	-0-	-0-
Nicholas Applegate Capital Mgmt. Convert & Income 2	6,500,000	-0-	-0-
Innovest Finanzdienstle	1,000,000	-0-	-0-
Baptist Health of South Florida	470,000	-0-	-0-
LB Series Fund, Inc. High Yield Portfolio	1,400,000	-0-	-0-
Lutheran Brotherhood High Yield Fund	1,100,000	-0-	-0-
Maystone Continium Master Fund, Ltd.	3,750,000	-0-	-0-
TQA Master Fund Ltd.	506,000	-0-	-0-

TQA Master Fund Plus Ltd	710,000	-0-	-0-
Zurich Inst. Benchmarks Master Fund Ltd.	74,000	-0-	-0-
Lexington Vantage Fund	10,000	-0-	-0-
Sphinz Fund	18,000	-0-	-0-
Xavex Convertible Arbitrage 7 Fund	120,000	-0-	-0-
LDG Limited	62,000	-0-	-0-
McMahon Securities Co. L.P.	725,000	-0-	-0-
UBS Securities LLC	1,500,000	-0-	-0-
O'Connor Global Convertible Arbitrage Master Limited LLC	3,500,000	-0-	-0-
Morgan Stanley Convertible Securities Trust	500,000	-0-	-0-
Amarath LLC	3,300,000	-0-	-0-
CNH CA Master Account, L.P.	3,000,000	-0-	-0-

(1): Amounts indicated may be in excess of the total amount registered due to sales or transfers exempt from the registration requirements of the Securities Act since the date upon which the selling holders provided to us the information regarding their notes and common stock.
(2): Unless otherwise noted, represents shares of common stock issuable upon conversion of notes. Represents less than 1% of the outstanding common stock.

With the exception of Lehman Brothers Inc. and Harris Nesbitt, none of the selling holders nor any of their affiliates, officers, directors or principal equity holders has held any position or office or has had any material relationship with us within three years of the date of this prospectus. Lehman Brothers Inc. and Harris Nesbitt were the initial purchasers of the notes described in this prospectus. The selling holders purchased the notes in private transactions on or after September 15, 2003. All of the notes were "restricted securities" under the Securities Act prior to this registration.

Information concerning the selling holders may change from time to time and any changed information will be set forth in supplements to this prospectus if and when necessary. In addition, the conversion rate and therefore, the number of shares of common stock issuable upon conversion of the notes, is subject to adjustment under certain circumstances. Accordingly, the aggregate principal amount of notes and the number of shares of common stock into which the notes are convertible may increase or decrease.

PLAN OF DISTRIBUTION

The selling holders and their successors, including their transferees, pledgees or donees or their successors, may sell the notes and the common stock into which the notes are convertible directly to purchasers or through underwriters, broker-dealers or agents, who may receive compensation in the form of discounts, concessions or commissions from the selling holders or the purchasers. These discounts, concessions or commissions as to any particular underwriter, broker-dealer or agent may be in excess of those customary in the types of transactions involved.

The notes and the common stock into which the notes are convertible may be sold in one or more transactions at fixed prices, at prevailing market prices at the time of sale, at prices related to the prevailing market prices, at varying prices determined at the time of sale, or at negotiated prices. These sales may be effected in transactions, which may involve crosses or block transactions:

•: on any national securities exchange or U.S. inter-dealer system of a registered national securities association on which the notes or the common stock may be listed or quoted at the time of sale;
•: in the over-the-counter market;
•: in transactions otherwise than on these exchanges or systems or in the over-the-counter market;
•: through the writing of options, whether the options are listed on an options exchange or otherwise; or
•: through the settlement of short sales.

In connection with the sale of the notes and the common stock into which the notes are convertible or otherwise, the selling holders may enter into hedging transactions with broker-dealers or other financial institutions, which may in turn engage in short sales of the notes or the common stock into which the notes are convertible in the course of hedging the positions they assume. The selling holders may also sell the notes or the common stock into which the notes are convertible short and deliver these securities to close out their short positions, or loan or pledge the notes or the common stock into which the notes are convertible to broker-dealers that in turn may sell these securities.

The aggregate proceeds to the selling holders from the sale of the notes or common stock into which the notes are convertible offered by them will be the purchase price of the notes or common stock less discounts and commissions, if any. Each of the selling holders reserves the right to accept and, together with their agents from time to time, to reject, in whole or in part, any proposed purchase of notes or common stock to be made directly or through agents. We will not receive any of the proceeds from this offering.

Our outstanding common stock is listed for trading on the Nasdaq National Market. We do not intend to list the notes for trading on any national securities exchange or on the Nasdaq National Market and can give no assurance about the development of any trading market for the notes.

In order to comply with the securities laws of some states, if applicable, the notes and common stock into which the notes are convertible may be sold in these jurisdictions only through registered or licensed brokers or dealers. In addition, in some states the notes and common stock into which the notes are convertible may not be sold unless they have been registered or qualified for sale or an exemption from registration or qualification requirements is available and is complied with.

The selling holders and any underwriters, broker-dealers or agents that participate in the sale of the notes and common stock into which the notes are convertible may be "underwriters" within the meaning of Section 2(11) of the Securities Act. Any discounts, commissions, concessions or profit they earn on any resale of the shares may be underwriting discounts and commissions under the Securities Act. Selling holders who are "underwriters" within the meaning of Section 2(11) of the Securities Act will be subject to the prospectus delivery requirements of the Securities Act. The selling holders have

acknowledged that they understand their obligations to comply with the provisions of the Exchange Act, and the rules thereunder relating to stock manipulation, particularly Regulation M.

In addition, any securities covered by this prospectus that qualify for sale pursuant to Rule 144 or Rule 144A of the Securities Act may be sold under Rule 144 or Rule 144A rather than pursuant to this prospectus. A selling holder may transfer, devise or gift these securities by other means not described in this prospectus.

To the extent required, the specific notes or common stock to be sold, the names of the selling holders, the respective purchase prices and public offering prices, the names of any agent, dealer or underwriter, and any applicable commissions or discounts with respect to a particular offer will be set forth in an accompanying prospectus supplement or, if appropriate, a post-effective amendment to the registration statement of which this prospectus is a part.

We entered into a registration rights agreement for the benefit of holders of the notes to register their notes and common stock under applicable federal and state securities laws under specific circumstances and at specific times. The registration rights agreement provides for cross-indemnification of the selling holders and us and their and our respective directors, officers and controlling persons against specific liabilities in connection with the offer and sale of the notes and the common stock, including liabilities under the Securities Act. We will pay certain costs and expenses associated with this registration of the notes and the common stock. These expenses include the SEC's filing fees, fees under state securities or "blue sky" laws, printing fees and professional fees (including counsel fees). The selling stockholders will pay all underwriting discounts, commissions, transfer taxes and certain other expenses associated with any sale of the notes and the common stock by them.

WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and special reports, proxy statements and other information with the SEC. You may read and copy any reports, statements or other information filed by us at the SEC's public reference room at Room 1024, Judiciary Plaza, 450 Fifth Street, N.W., Washington, D.C. 20549. You can request copies of these documents by contacting the SEC and paying a fee for the copying costs. Please call the SEC at 1-800-SEC-0330 for further information on the public reference room. You also may inspect copies of these materials at the reading room of the library of the National Association of Securities Dealers, Inc., 1735 K Street, N.W., Washington, D.C. 20006. Our SEC filings are also available to the public from commercial document retrieval services and at the SEC's web site at "http://www.sec.gov."

We "incorporate by reference" into this prospectus certain information we file with the SEC, which means that we can disclose important information to you by referring you to another document we filed with the SEC. The information incorporated by reference is an important part of this prospectus, and information that we file later with the SEC will automatically update and supersede this information. We incorporate by reference the documents listed below and any future filings we will make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, after the date of this prospectus but before the end of any offering made under this prospectus:

•: our Current Report on Form 8-K, filed with the SEC on September 5, 2003 (the "Form 8-K");
•: our Current Report on Form 8-K, filed with the SEC on September 16, 2003;
•: our Quarterly Reports on Form 10-Q for the quarters ended June 30, 2003 and March 31, 2003;
•: our Definitive Proxy Statement on Schedule 14A as filed with the SEC on April 30, 2003, excluding the information contained in such proxy statement under the captions "Executive Compensation and Other Information—Ten-Year Option Repricings," "Stock Price Performance Graph," "Compensation Committee Report on Executive Compensation" and "Report of the Audit Committee," which are not incorporated by reference in this prospectus; and
•: our Annual Report on Form 10-K for the fiscal year ended December 31, 2002, as amended and superseded by Items 5.B and 7 of the Form 8-K;

We will furnish without charge to you, upon written or oral request, a copy of any or all of the documents described above, except for exhibits, unless the exhibits are specifically incorporated by reference into the prospectus. You should direct your requests to: Primus Telecommunications Group, Incorporated, 1700 Old Meadow Road, McLean, VA 22102, Attention: Thomas R. Kloster, Senior Vice President.

WE HAVE AUTHORIZED NO ONE TO GIVE ANY INFORMATION OR TO MAKE ANY REPRESENTATIONS NOT CONTAINED IN THIS PROSPECTUS. YOU SHOULD RELY ONLY ON THE INFORMATION PROVIDED IN THIS PROSPECTUS OR INCORPORATED BY REFERENCE THEREIN. YOU MUST NOT RELY ON ANY UNAUTHORIZED INFORMATION.

THIS PROSPECTUS DOES NOT OFFER TO SELL OR BUY ANY NOTES OR SHARES OF COMMON STOCK IN ANY JURISDICTION WHERE IT IS UNLAWFUL. YOU SHOULD NOT ASSUME THAT THE INFORMATION IN THIS PROSPECTUS IS ACCURATE AS OF ANY DATE OTHER THAN THE DATE ON THE FRONT OF THIS PROSPECTUS.

FORWARD-LOOKING INFORMATION

Certain statements included or incorporated by reference into this prospectus and elsewhere concerning Primus constitute "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Such statements are based on current expectations, and are not strictly historical statements. Forward-looking statements include, without limitation, statements set forth in this prospectus and elsewhere regarding, among other things:

•: our expectations of future growth, revenue, foreign revenue contributions and net income, as well as income from operations, earnings per share, cost reduction efforts, cash flow, network development, Internet services development, traffic development, capital expenditures, selling, general and administrative expenses, goodwill impairment charges, service introductions and cash requirements;
•: our financing, refinancing and/or debt repurchase, restructuring or exchange plans or initiatives;
•: our liquidity and debt service forecasts;
•: assumptions regarding stable currency exchange rates;
•: management's plans, goals, expectations, guidance, objectives, strategies, and timing for future operations, acquisitions, product plans and performance;
•: the revenue or other impact of our acquisition of the SME customer base of C&W in the United States; and
•: management's assessment of market factors.

Factors and risks, including certain of those described in greater detail herein, that could cause actual results or circumstances to differ materially from those set forth or contemplated in forward-looking statements include, without limitation:

•: changes in business conditions;
•: fluctuations in the exchange rates of currencies, particularly any strengthening of the United States dollar relative to foreign currencies of the countries where we conduct our foreign operations;
•: adverse interest rate developments;
•: fluctuations in prevailing trade credit terms or revenues due to the adverse impact of, among other things, further telecommunications carrier bankruptcies or adverse bankruptcy related developments affecting our large carrier customers;
•: the possible inability to raise additional capital when needed, or at all;
•: the inability to reduce, repurchase, exchange or restructure debt significantly, or in amounts sufficient to conduct regular ongoing operations;
•: changes in the telecommunications or Internet industry;
•: adverse tax rulings from applicable taxing authorities;
•: digital subscriber line (DSL), Internet and telecommunications competition;
•: changes in financial, capital market and economic conditions;
•: changes in service offerings or business strategies;

•: difficulty in migrating or retaining customers, including former C&W customers associated with our recent acquisition of this customer base, or integrating other assets;
•: difficulty in providing voice-over-Internet protocol services;
•: changes in the regulatory schemes or requirements and regulatory enforcement in the markets in which we operate;
•: restrictions on our ability to follow certain strategies or complete certain transactions as a result of our capital structure or debt covenants;
•: risks associated with our limited DSL, Internet and Web hosting experience and expertise;
•: entry into developing markets;
•: the possible inability to hire and/or retain qualified sales, technical and other personnel, and to manage growth;
•: risks associated with international operations;
•: dependence on effective information systems;
•: dependence on third parties to enable us to expand and manage our global network and operations;
•: dependence on the implementation and performance of our global asynchronous transfer mode + Internet protocol communications network;
•: adverse outcomes of outstanding litigation matters; and
•: the outbreak or escalation of hostilities or terrorist acts and adverse geopolitical developments.

As such, actual results or circumstances may vary materially from such forward-looking statements or expectations. Readers are also cautioned not to place undue reliance on these forward-looking statements which speak only as of the date these statements were made. We are not necessarily obligated to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

You are advised, however, to consult the discussion of risks and uncertainties under "Risk Factors" in this prospectus and under "Management's Discussion and Analysis of Financial Condition and Results of Operations—Liquidity and Capital Resources—Short- and Long-Term Liquidity Considerations and Risks" and "Business—Legal Proceedings" in the Form 8-K and in our Form 10-K and Forms 10-Q filed with the SEC. See "Where You Can Find More Information." These are the principal factors that we think could cause our actual results to differ materially from expected results, but other factors could also adversely affect our business and the value of your investment in our securities.

LEGAL MATTERS

Cooley Godward LLP, Reston, Virginia, will pass upon legal matters for us regarding the validity of the notes and the shares of common stock issuable upon conversion of the notes.

EXPERTS

The consolidated financial statements and the related financial statement schedule of Primus Telecommunications Group, Incorporated and subsidiaries, incorporated in this prospectus by reference from Primus Telecommunications Group, Incorporated's Current Report on Form 8-K, as filed with the SEC on September 5, 2003, have been audited by Deloitte & Touche LLP, independent auditors, as stated in their report dated February 27, 2003 (August 28, 2003 as to the effects of the adoption of Statement of Financial Accounting Standard (SFAS) No. 145 described in Note 2), which report expresses an unqualified opinion and includes an explanatory paragraph referring to the adoption of SFAS No. 142, "Goodwill and Other Intangible Assets" and SFAS No. 145, "Rescission of FASB Statements No. 4, 44, and 64, amendment of FASB Statement No. 13, and Technical Corrections," which is incorporated herein by reference, and has been so incorporated in reliance upon the report of such firm given upon their authority as experts in accounting and auditing.

PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 14. OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION

The following table sets forth the costs and expenses, other than underwriting discounts and commissions, payable by the registrant in connection with the distribution of the notes and common stock being registered. All amounts are estimated, except the SEC Registration Fee, and the Nasdaq National Market Filing Fee:

SEC Registration Fee	$	10,679
Accounting Fees	$	25,000
Legal Fees and Expenses	$	50,000
Printing and Engraving	$	10,000
Miscellaneous	$	5,000

Total	$	100,679

ITEM 15. INDEMNIFICATION OF DIRECTORS AND OFFICERS

Section 145 of the Delaware General Corporation Law (the "DGCL") permits each Delaware business corporation to indemnify its directors, officers, employees and agents against liability for each such person's acts taken in his or her capacity as a director, officer, employee or agent of the corporation if such actions were taken in good faith and in a manner which he or she reasonably believed to be in or not opposed to the best interests of the corporation, and with respect to any criminal action, if he or she had no reasonable cause to believe his or her conduct was unlawful. Article X of our Amended and Restated By-Laws provides that we, to the full extent permitted by Section 145 of the DGCL, shall indemnify all of our past and present directors and may indemnify all of our past or present employees or other agents. To the extent that a director, officer, employee or agent of ours has been successful on the merits or otherwise in defense of any action, suit or proceeding referred to in such Article X, or in defense of any claim, issue or matter therein, he or she shall be indemnified by us against actually and reasonably incurred expenses in connection therewith. Such expenses may be paid by us in advance of the final disposition of the action upon receipt of an undertaking to repay the advance if it is ultimately determined that such person is not entitled to indemnification.

As permitted by Section 102(b)(7) of the DGCL, Article 11 of our Amended and Restated Certificate of Incorporation provides that no director shall be liable to us for monetary damages for breach of fiduciary duty as a director, except for liability:

(i): for any breach of the director's duty of loyalty to us or our stockholders,
(ii): for acts or omissions not in good faith or which involve intentional misconduct or a knowing violation of law,
(iii): for the unlawful payment of dividends on or redemption of our capital stock; or
(iv): for any transaction from which the director derived an improper personal benefit.

We have obtained a policy insuring us and our directors and officers against certain liabilities, including liabilities under the Securities Act.

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ITEM 16. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES

(a): Exhibits.

4.1		Indenture dated as of September 15, 2003 between the Registrant and Wachovia Bank, National Association, including therein the forms of the notes.
4.2		Registration Rights Agreement dated as of September 15, 2003 between the Registrant, Lehman Brothers Inc. and Harris Nesbitt Corp.
5.1		Opinion of Cooley Godward LLP.
12.1		Computation of Ratio of Earnings to Fixed Charges.
23.1		Consent of Deloitte & Touche LLP, Independent Auditors.
23.2		Consent of Cooley Godward LLP (included in Exhibit 5.1).
24.1		Power of Attorney (see page II-3).
25.1		Form T-1. Statement of Eligibility under the Trust Indenture Act of Wachovia Bank, National Association.

(b): Financial Statement Schedules

Consolidated Schedules are omitted because they are not applicable, or because the information is included in the Schedule, Financial Statements or the Notes thereto, which are incorporated by reference from the registrant's Annual Report on Form 10-K for the fiscal year ended December 31, 2002 and Current Report on Form 8-K filed with the SEC on September 5, 2003.

ITEM 17. UNDERTAKINGS.

The undersigned Registrant hereby undertakes:

(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this Registration Statement

(i): To include any prospectus required by Section 10(a)(3) of the Securities Act;
(ii): To reflect in the prospectus any facts or events arising after the effective date of this Registration Statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in this Registration Statement. Notwithstanding the foregoing, any increase or decrease in the volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than 20 percent change in the maximum aggregate offering price set forth in the "Calculation of Registration Fee" table in the effective Registration Statement; and
(iii): To include any material information with respect to the plan of distribution not previously disclosed in this Registration Statement or any material change to such information in this Registration Statement;

provided, however, that paragraphs (1)(i) and (1)(ii) do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in periodic reports filed by the Company pursuant to Section 13 or Section 15(d) of the Exchange Act, that are incorporated by reference in this Registration Statement.

(2) That, for the purposes of determining any liability under the Securities Act, each post-effective amendment that contains a form of prospectus shall be deemed to be a new registration statement

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relating to the securities offered therein, and the offering of such securities at the time shall be deemed to be the initial bona fide offering thereof.

(3) To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

The Registrant hereby undertakes that, for purposes of determining any liability under the Securities Act, each filing of the Registrant's annual report pursuant to Section 13(a) or 15(d) of the Exchange Act (and, where applicable, each filing of an employee benefit plan's annual report pursuant to Section 15(d) of the Exchange Act) that is incorporated by reference in this Registration Statement shall be deemed to be a new registration statement relating to the securities offered therein and the offering of such securities at the time shall be deemed to be the initial bona fide offering thereof.

Insofar as indemnification for liabilities arising under the Securities Act may be permitted to directors, officers and controlling persons of the Registrant pursuant to the indemnification provisions described herein, or otherwise, the Registrant has been advised that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the Registrant of expenses incurred or paid by a director, officer or controlling person of the Registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the Registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

The undersigned registrant hereby undertakes to file an application for the purpose of determining the eligibility of the trustee to act under Subsection (a) of Section 310 of the Trust Indenture Act in accordance with the rules and regulations prescribed by the Commission under Section 305(b)(2) of the Trust Indenture Act.

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SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the city of McLean, Commonwealth of Virginia, on October 22, 2003.

		PRIMUS TELECOMMUNICATIONS GROUP, INCORPORATED
		By:		/s/ K. PAUL SINGH K. Paul Singh Chairman, President and Chief Executive Officer

POWER OF ATTORNEY

Each person whose signature appears below constitutes and appoints K. Paul Singh, John F. DePodesta and Neil L. Hazard his or her true and lawful attorney-in-fact and agent, each acting alone, with full power of substitution and resubstitution, for him or her and in his or her name, place and stead, in any and all capacities, to sign any or all amendments (including post-effective amendments and registration statements filed pursuant to Rule 462 under the Securities Act) to the Registration Statement on Form S-3, and to file the same, with all exhibits thereto, and all documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorney-in-fact and agent, full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorney-in-fact and agent, or his or her substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed by the following persons in the capacities and on the dates indicated.

Signatures	Title	Date

/s/ K. PAUL SINGH K. Paul Singh	Chairman, President, Chief Executive Officer (Principal Executive Officer)	October 22, 2003
/s/ JOHN F. DEPODESTA John F. DePodesta	Executive Vice President, Secretary and Director	October 22, 2003
/s/ NEIL L. HAZARD Neil L. Hazard	Executive Vice President, Chief Operating Officer and Chief Financial Officer (Principal Financial Officer)	October 22, 2003
/s/ TRACY R. BOOK Tracy R. Book	Vice President — Corporate Controller (Principal Accounting Officer)	October 22, 2003
/s/ DAVID E. HERSHBERG David E. Hershberg	Director	October 22, 2003

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/s/ NICK EARLE Nick Earle	Director	October 22, 2003
/s/ PRADMAN P. KAUL Pradman P. Kaul	Director	October 22, 2003
/s/ JOHN G. PUENTE John G. Puente	Director	October 22, 2003
/s/ DOUGLAS M. KARP Douglas M. Karp	Director	October 22, 2003
/s/ PAUL G. PIZZANI Paul G. Pizzani	Director	October 22, 2003

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EXHIBIT INDEX

4.1		Indenture dated as of September 15, 2003 between the Registrant and Wachovia Bank, National Association, including therein the forms of the notes.
4.2		Registration Rights Agreement dated as of September 15, 2003 between the Registrant, Lehman Brothers Inc. and Harris Nesbitt Corp.
5.1		Opinion of Cooley Godward LLP.
12.1		Computation of Ratio of Earnings to Fixed Charges.
23.1		Consent of Deloitte & Touche LLP, Independent Auditors.
23.2		Consent of Cooley Godward LLP (included in Exhibit 5.1).
24.1		Power of Attorney (see page II-3).
25.1		Form T-1. Statement of Eligibility under the Trust Indenture Act of Wachovia Bank, National Association.

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QuickLinks

TABLE OF CONTENTS
SUMMARY
PRIMUS
SECURITIES TO BE OFFERED
RISK FACTORS
USE OF PROCEEDS
DIVIDEND POLICY
SELECTED FINANCIAL DATA
DESCRIPTION OF THE NOTES
DESCRIPTION OF CAPITAL STOCK
MATERIAL UNITED STATES FEDERAL INCOME TAX CONSEQUENCES
SELLING SECURITY HOLDERS
PLAN OF DISTRIBUTION
WHERE YOU CAN FIND MORE INFORMATION
FORWARD-LOOKING INFORMATION
LEGAL MATTERS
EXPERTS
PART II INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 14. OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION

ITEM 15. INDEMNIFICATION OF DIRECTORS AND OFFICERS

ITEM 16. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES

ITEM 17. UNDERTAKINGS.

SIGNATURES
POWER OF ATTORNEY
EXHIBIT INDEX