Sonus Growth in Japan Continues Dramatic Increase

CHELMSFORD, Mass., December 20, 2005 – Sonus Networks, Inc. (Nasdaq: SONS), a leading supplier of service provider voice over IP (VoIP) infrastructure solutions, announced today that market research firms Synergy Research Group and Infonetics Research have reported that Sonus is leading Japan's migration to VoIP with key customer deployments throughout the telecommunications, cable, Internet Service Provider (ISP), and wireless industries.

"Sonus' leadership position in the rapidly growing Japanese market is a testament to the Company's vision, our ability to execute, and our commitment to this important region of the world," said Hassan Ahmed, chairman and CEO, Sonus Networks. "Asia-Pacific has been one of the first regions to embrace the benefits of VoIP and harness the power of these technologies to deliver innovative services to consumers, and Japan in particular has accelerated its migration to an all-IP infrastructure. As a company, we are dedicated to ensuring our customers' success as they extend their service capabilities in Japan and throughout Asia-Pacific."

A recent report entitled "Q3 2005 Service Provider VoIP Japan Market Shares," issued by Synergy Research Group, reveals that based on revenue Sonus is the clear leader in the carrier VoIP market in Japan with total media gateway market share of 61.1% and dominates the high density media gateway industry with 81.1% of the total market.

"Sonus' performance in Japan is truly impressive," said Jeremy Duke, president and CEO, Synergy Research Group. "Sonus' first mover advantage, sophisticated field-tested technology, strategic partnerships, and the expertise of its professional services team have earned Sonus a highly respected position in the Japanese market and this is reflected in their substantial market share position."

Infonetics Research also released its third quarter market share analysis, which shows Sonus substantially increasing its market share in the total Asia-Pacific region due to its success in Japan. Infonetics named Sonus as the market share leader in both the total carrier-class media gateway and high density gateway revenue.

"Sonus has an enviable position of being firmly entrenched in Japan's VoIP industry, particularly in the Voice over Broadband (VoBB) market," said Teresa Mastrangelo, analyst broadbandtrends.com. "With nearly 10 million subscribers, Japan continues to lead the world in VoBB subscribers, and shows no sign of slowing down. Over the past 12 months, Japan's VoBB subscribers have grown 39 percent. Sonus' success in this region is a significant indicator of the Company's ability to deliver reliable solutions capable of scaling to meet the demand of one of the world's fastest growing markets."

About Sonus Networks

Sonus Networks, Inc. is a leading provider of voice over IP (VoIP) infrastructure solutions for wireline and wireless service providers. With its comprehensive IP Multimedia Subsystem (IMS) solution, Sonus addresses the full range of carrier applications, including residential and business voice services, wireless voice and multimedia, trunking and tandem switching, carrier interconnection and enhanced services. Sonus' voice infrastructure solutions are deployed in service provider networks worldwide. Founded in 1997, Sonus is headquartered in Chelmsford, Massachusetts. Additional information on Sonus is available at http://www.sonusnet.com.

This release may contain forward-looking statements regarding future events that involve risks and uncertainties. Readers are cautioned that these forward-looking statements are only predictions and may differ materially from actual future events or results. Readers are referred to the “Risk Factors” section of Sonus' Annual Report on Form 10-K, dated March 15, 2005, and the “Cautionary Statements” section of Sonus' Quarterly Report on Form 10-Q, dated November 8, 2005, both filed with the SEC, which identify important risk factors that could cause actual results to differ from those contained in the forward-looking statements. Risk factors include among others: the impact of material weaknesses in our disclosure controls and procedures and our internal control over financial reporting on our ability to report our financial results timely and accurately; the unpredictability of our quarterly financial results; risks associated with our international expansion and growth; consolidation in the telecommunications industry; and potential costs resulting from pending securities litigation against the company. Any forward-looking statements represent Sonus' views only as of today and should not be relied upon as representing Sonus' views as of any subsequent date. While Sonus may elect to update forward-looking statements at some point, Sonus specifically disclaims any obligation to do so.

Sonus is a registered trademark of Sonus Networks. All other company and product names may be trademarks of the respective companies with which they are associated.