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Becomes First Vendor to Gain Both BT IUP and UK ISUP Blue Stamps

SWINDON, UK, August 24, 2004 - Sonus Networks (Pink Sheets: SONS), a leading supplier of service provider voice over IP (VoIP) infrastructure solutions, today announced that it has completed the second stage of rigorous interoperability testing of its products with BT's technology and IT operations division, BT Exact. Sonus' solution, consisting of the InsignusTM Softswitch, GSX9000TM Open Services Switch and the Sonus InsightTM Management System, has now received the BT Exact 'Blue Stamp' of approval for UK ISUP compliance.

Any telecommunications service provider wishing to interconnect with BT's UK network must ensure that its own network infrastructure complies with UK ISUP and/or BT IUP, making these standards an important benchmark for vendors targeting the UK market. Sonus announced compliance with BT IUP, a variant of Signaling System Seven (SS7), in October 2003.

"Today's announcement is further testament to our commitment to the UK market and to standards-based interoperability," said Steve Edwards, chief marketing officer and general manager, EMEA, Sonus Networks. "BT Exact's testing programme has confirmed the experience of our customers: that Sonus' softswitch solution is a robust platform for delivering next-generation voice services."

BT Exact's interworking tests are designed to exercise all aspects of a solution's expected live behaviour, including its ability to handle all call types, and to respond correctly to maintenance actions and failure of other equipment in the network. Equipment is also tested under 'provocative' conditions such as the receipt of specific message contents or sequences, or failures on the switch to which it is connected. To achieve approval, Sonus' solution was tested for its conformance to the relevant standards and its ability to work reliably when connected into networks that contain other manufacturers' products.

"Sonus Networks is the first company to complete 'Blue Stamp' accreditation for both BT IUP and UK ISUP," said Paul Challener, head of networks and testing portfolio at BT Exact. "Sonus' solution has been shown to operate reliably under all foreseeable network conditions and has demonstrated compliance with the relevant standards for interconnection with BT's UK 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 Open Services ArchitectureTM (OSA), Sonus delivers end-to-end solutions addressing a full range of carrier applications, including trunking and tandem switching, residential and business access, network border switching and enhanced services. Sonus' 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 Chelmsford, Massachusetts. Additional information on Sonus is available at http://www.sonusnet.com.

About BT

BT Group plc is the holding company for an integrated group of communications businesses and is listed on stock exchanges in London and New York. British Telecommunications plc (BT) is a wholly-owned subsidiary of BT Group and encompasses virtually all businesses and assets of the BT Group.

BT is one of the world's leading providers of communications solutions serving customers in Europe, the Americas and Asia Pacific. Its principal activities include network centric Information and Communications Technology (ICT) solutions, local, national and international telecommunications services, and higher-value broadband and internet products and services.

BT consists principally of three lines of business:

• BT Retail, providing fixed and mobile communications services and solutions to over 20 million business and residential customers in the UK. It is also a leading UK internet services provider.
• BT Wholesale, providing network services and solutions within the UK to more than 600 fixed and mobile operators and service providers including the provision of broadband, private circuits and PSTN.
• BT Global Services, providing ICT services internationally to meet the needs of multi-site organisations with European operations. BT Global Services operates in 136 countries and also offers international carrier services.

In the year ended 31 March 2004, BT Group's turnover was £18,519 million with profit before goodwill amortisation, exceptional items and taxation of £2,013 million. For more information, visit www.btplc.com

About BT Exact

BT Exact is BT's technology and IT operations division. It specialises in telecommunications engineering, leading-edge network design, IT system and application development and has extensive expertise in business consulting and human factors. Its knowledge helps its customers across BT Group and in selected other businesses gain maximum advantage from their investments in communications networks and IT systems, develop new capabilities and open new opportunities.

BT Exact brings together the technological expertise of BT's research laboratories and the operational experience of the teams that design and operate BT's IT systems. Backed by a team of over 6,000 technologists, it is active and influential in setting global standards. BT Exact builds on the insights and expertise developed by its research to address the demands of the next-generation internet, as well as advanced data services, information and network security, and software systems to support communications networks worldwide. BT Exact has people based worldwide - including locations across the UK and in Asia, continental Europe, and North America. For more information about BT Exact, please go to www.bt.com/btexact

Sonus is a registered trademark of Sonus Networks. Open Services Architecture, GSX9000 and Insignus are trademarks of Sonus Networks. All other trademarks, service marks, registered trademarks, or registered service marks are the property of their respective owners.