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CHELMSFORD, Mass., March 13, 2006 - Sonus Networks, Inc. (Nasdaq: SONS), a leading supplier of service provider Voice over IP (VoIP) infrastructure solutions, today reported its financial results for the fourth quarter and fiscal year ended December 31, 2005.

Revenues for the fourth quarter of fiscal 2005 were $57.2 million compared with $45.1 million in the same period last year, an increase of 27%. Net income for the fourth quarter of fiscal 2005 was $5.0 million, or $0.02 per diluted share, compared with net income for the fourth quarter of fiscal 2004 of $6.3 million, or $0.02 per diluted share.

Revenues for fiscal year 2005 were $194.6 million compared with $170.7 million for fiscal year 2004, an increase of 14%. Net income for fiscal year 2005 was $8.4 million, or $0.03 per diluted share, compared with net income for fiscal year 2004 of $24.5 million, or $0.10 per diluted share.

"2005 was a strong year for Sonus, culminating with robust revenue, order and shipments growth in the fourth quarter," said Hassan Ahmed, chairman and CEO, Sonus Networks. "We are aggressively driving growth across all areas of the Company by broadening our market reach into new regions, introducing new innovative technology, expanding our footprint within our existing customers' networks and winning significant new deployments with operators in each of our global theaters." Ahmed continued, "Today's announcement that KDDI, a major carrier in Japan, is deploying a Sonus packet voice solution to replace its legacy infrastructure represents an important milestone for Sonus and the industry overall."

In a press release issued earlier today, Sonus announced that it was selected by KDDI, a leading telecommunication service provider in Japan, for a multi-million dollar contract as the exclusive vendor for its convergence-enabled packet voice network (see related announcement "KDDI Selects Sonus Networks to Deploy Largest VoIP Network in Japan"). In the first phase of this project, KDDI is deploying a full suite of Sonus' industry-leading solutions, including the GSX9000TM Open Services Switch, the PSX™ Call Routing Server and the Sonus InsightÔ 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 its Sonus-based VoIP network.

Fourth Quarter 2005 Summary

In the fourth quarter of 2005, Sonus Networks continued to broaden its customer base and expand its presence throughout the Europe, Middle East and Africa region. To address and service the growing market opportunity throughout Europe, Sonus Networks announced the opening of a new operations center in Prague, Czech Republic. The establishment of an office in the Czech Republic is in direct response to increased demand for Sonus solutions throughout the region. In addition to Prague, the Company now has a regional sales and support presence throughout several countries in Western Europe, including the United Kingdom, France and Germany.

Sonus announced that it was awarded a multi-million dollar contract for the worldwide expansion of T-Systems' business VoIP network. T-Systems is the business customer division of the Deutsche Telekom Group and one of Europe's leading providers of information and communications technology.

The Company reported that in tandem with its recently announced partner, TNN Networks, Sonus is delivering a complete IMS (IP Multimedia Subsystem)-ready voice over broadband (VoBB) solution to 012 Golden Lines, a leading Israeli Internet Service Provider (ISP) and a provider of international voice services for enterprises and consumers.

In Japan, Sonus continues to lead the service provider VoIP market. Synergy Research Group reported that in the third quarter of 2005, Sonus accounted for more than 61% of the total media gateway industry and more than 80% of the high density media gateway industry. Japan, which has been a key driver in global VoBB adoption, continues to be a strategic focus for Sonus.

Globally, Sonus continued to build on its worldwide leadership position. Sonus was recognized as the market share leader of carrier-class VoIP equipment for the third quarter of 2005 by Infonetics Research and Synergy Research Group. By the end of the year, according to research conducted by iLocus, Sonus' industry-leading solutions were carrying in excess of 17 billion minutes of VoIP traffic per month, a 70 percent increase compared to December 2004.

Sonus continued to drive market penetration for IP-based solutions in the fourth quarter with a new technology introduction, the Sonus-certified Consumer Voice over Broadband (c-VoBB) Solution, the first in a series of integrated IMS-ready solutions designed to enable the rapid deployment of next-generation services. The Sonus c-VoBB solution empowers network operators to enter the consumer VoIP market in a cost-efficient manner and supports a broad portfolio of IMS-ready applications.

Sonus also announced the availability of the Sonus Voice Portal, an interactive voice response system for managing consumer voice profile data. The Sonus Voice Portal was the first application created with and managed by Sonus' IMX application platform, a web-based multimedia environment that enables wireline and wireless service providers to rapidly develop, integrate, launch, and manage enhanced telecommunication applications and services.

To further promote consumer adoption of VoIP services, Sonus aligned with other industry leaders, including EarthLink, Google, Level 3, Pulver.com, Skype and USA Datanet, as founding members of the Internet Voice Campaign (IVC). Part of the VON Coalition, a non-profit, VoIP industry advocacy organization, the Internet Voice Campaign is designed to raise awareness and help educate consumers about the benefits of IP-based voice solutions.

"In the year ahead, we aim to capitalize on our increased momentum to foster demand for our solutions both in markets where Sonus has a long-standing leadership position and in those that are just beginning to embrace the benefits of VoIP," said Ahmed. "Through the success of our customers and awareness campaigns like the IVC, consumers are beginning to recognize that VoIP has the power to change the way we communicate. It's an exciting time in the evolution of communications networks, and Sonus continues to lead the world's migration to IMS-based networks."

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 "Cautionary Statements" section of the Company's most recent quarterly report on Form 10-Q filed with the SEC, which identifies 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, Inc. Sonus GSX9000 Open Services Switch, PSX Call Routing Server, SGX Signaling Gateway, and the Sonus Insight Management System are trademarks of Sonus Networks, Inc. All other company and product names may be trademarks of the respective companies with which they are associated.