KDDI Selects Sonus Networks To Deploy Largest VoIP Network In Japan

Leading Japanese Broadband Provider Plans to Build VoIP Network to Provide High Value-Added Telecommunications Services

CHELMSFORD, MA and TOKYO, JAPAN, March 13, 2006 - Sonus Networks (Nasdaq: SONS), a leading supplier of service provider voice over IP (VoIP) infrastructure solutions, today announced that KDDI, a leading telecommunication service provider in Japan, selected Sonus Networks as the exclusive vendor for their convergence-enabled packet voice network.

In the first phase of this multi-million dollar contract, KDDI is deploying Sonus' industry-leading architecture, including the GSX9000TM Open Services Switch, the PSX™ Call Routing Server and the Sonus InsightTM Element Management System. The new packet voice network will deliver enhanced voice services to one of the most technologically advanced societies in the world and is planned to be the largest IP telephony network in Japan.

“By 2008, KDDI plans to have 100 percent of its long-distance traffic on a Sonus-based VoIP network,” said Yukio Takahashi, General Manager, IP Network Engineering Division, Corporate Technology Sector, KDDI Corporation. “Sonus has demonstrated a clear commitment to the Japanese market, with a proven record of delivering superior products and customer support. With this implementation, we will realize substantial operational savings and have the flexibility to expand our IP-based network to offer feature-rich next generation services, thereby delivering enhanced customer loyalty and satisfaction.”

In the first phase of this deployment, KDDI is deploying Sonus' solution to deliver long distance functionality for their consumer voice service plans -- Metal Plus, MYLINE and Hikari Plus. In future phases of the deployment, KDDI will expand its ubiquitous network to deliver triple-play services to customers nationwide.

“KDDI's deployment represents a major milestone in the evolution of the market and reaffirms their leadership position in the broadband communications industry,” said Hassan Ahmed, chairman and CEO, Sonus Networks. “KDDI has taken a very aggressive approach because they recognize both the immediate and longer term benefits to their business and their customers. We are very proud that KDDI has selected Sonus as the foundation for their new VoIP network.”

“Sonus Networks is uniquely positioned to effectively enable KDDI's transition to a VoIP network because of our experience in the Japanese market and the proven scalability and reliability of our solutions in both wireline and wireless networks. By deploying a packet voice network from Sonus, KDDI can be confident that they will continue to deliver the same high levels of service that their customers have come to expect. Additionally, the Sonus solution enables KDDI to rapidly expand their network into new segments of the market and to deliver new services,” said Takayuki Oshima, Managing Director of Japan, Sonus Networks.

About KDDI

KDDI Corporation (http://www.kddi.com/english) is the only single company in Japan that can provide full-service telecommunications and answer all customer needs from fixed-line to mobile telecommunications as well as comprehensive Internet services. Taking full advantage of the integrated strengths, the company realizes the convergence of Mobile and the Internet to create a highly advanced telecommunications environment and provide customers with unsurpassed service. KDDI restarted with the merger of DDI, KDD and IDO on October 1, 2000 to combine the cumulative business resources of three companies that include not only extensive achievements in the fields of domestic, international and mobile communications, but also world-renowned R&D capabilities and a cutting-edge infrastructure realized by an optical-fiber network.

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.

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