TOKYO, Japan and WESTFORD, Mass., May 6, 2002 - KDDI Corporation and Sonus Networks (Nasdaq: SONS) today announced that KDDI has selected Sonus to provide packet voice infrastructure solutions to support the delivery of voice over IP (VoIP) services over KDDI's broadband network. By deploying Sonus' industry-leading media gateway, softswitch and management solutions, KDDI will be able to cost-effectively deliver a range of SIP-based voice services over their high-speed fiber optic infrastructure.

To meet the growing demand for high-capacity Internet connections to consumers' homes, KDDI delivers broadband services over fiber to the home. As part of this offering, KDDI provides users IP telephones to replace their conventional handsets, as well as a high-speed Internet environment supporting a range of next-generation services such as VoIP, video on demand, streaming video, music download services, network gaming, and remote education.

To support VoIP services, working together with Sonus and its distribution partner, Nissho Electronics, a leading network integrator in Japan, KDDI has implemented Sonus' award-winning packet voice solutions including the GSX9000(TM) Open Services Switch, the Insignus(TM) Softswitch and the Sonus Insight(TM) Element Management System. Leveraging the flexible, robust Session Initiation Protocol (SIP), KDDI offers on-net calling services, as well as IP-to-PSTN and PSTN-to-IP calling, on the Sonus infrastructure.

"In step with the rapid growth of the Internet user population, KDDI is making a full-scale transition to delivering broadband access services," said Hassan Ahmed, president and CEO, Sonus Networks. "We are very excited about our deployment with KDDI, and are pleased to be collaborating with them to deliver next-generation services and applications to their customers."

About KDDI Corporation

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 packet voice infrastructure products for the new public network. With its Open Services Architecture (OSA), Sonus delivers end-to-end solutions addressing a full range of carrier applications, including trunking, residential access and Centrex, tandem switching, and IP voice termination, as well as enhanced services. Sonus' award-winning voice infrastructure solutions, including media gateways, softswitches and network management systems, are deployed in service provider networks worldwide. Sonus, founded in 1997, is headquartered in Westford, Massachusetts. Additional information on Sonus is available at http://www.sonusnet.com.

This release may contain projections or other forward-looking statements regarding future events or the future financial performance of Sonus 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 Sonus' 2001 Annual Report on Form 10-K, dated March 27, 2002 and filed with the SEC, which identifies important risk factors that could cause actual results to differ from those contained in the forward-looking statements. These risk factors include, among others, the adverse effect of recent developments in the telecommunications industry, the weakened financial position of many emerging service providers, Sonus' ability to grow its customer base, dependence on new product offerings, market acceptance of its products, rapid technological and market change and manufacturing and sourcing risks.

GSX9000, Insignus, Sonus Insight and Open Services Architecture are trademarks of Sonus Networks. All other company and product names may be trademarks of the respective companies with which they are associated.