VON Europe 2001 - Booth No. 404/503

SWINDON, UK. June 11, 2001 – Sonus Networks, Inc. (Nasdaq: SONS) and Tango Telecom Ltd today announced at VON Europe 2001 that they are working together to enable network operators to offer IN (Intelligent Network) based valued added services over Sonus-based network infrastructure. Tango and Sonus will jointly market the complete IN services solution.

The combination of Sonus' family of voice infrastructure solutions and Tango Telecom's INgate will allow network operators to offer legacy IN services such as VPN, Freephone, Number Portability and Carrier Selection in Sonus packet voice networks. IN-based services are extensively used by European and Asian network carriers. 

The joint solution leverages network operators' existing IN infrastructure investment, which reduces operators' costs of offering services. It also allows operators to deliver uniform services across both their traditional PSTN infrastructure and their converged Sonus infrastructure, and provides operators with a single management point for services in both traditional and converged networks. The backwards compatibility with existing service infrastructure and management systems will simplify migration to an all Sonus network infrastructure.

Tango Telecom is a member of Sonus' worldwide OSPA program. Interoperability trials between Tango's INgate and Sonus Networks packet voice solutions including PSX-6000TM and GSX-9000TM are currently underway in Swindon, UK with a focus on European and Asian network services. 

"Tango is excited to be working with the global leader in packet voice infrastructure solutions," declared Thaddeus Albers, Business Development Manager at Tango Telecom. "The total solution we are delivering will provide network operators with the best of both worlds: the existing high end services of the PSTN network and cost savings inherent in the converged Sonus-based network."

"With the current widespread deployment of traditional IN based services, this total solution will clearly differentiate our ability to supply the needs of the global market and we expect it to help us facilitate the specific evolutionary needs of European and Asian operators," stated Barry Bonnett, EMEA Vice President at Sonus Networks.

About Tango

Founded in 1999, Tango Telecom focuses on providing value added services for current and next generation operators. The Tango team has over a century of telecommunications industry experience relevant to the enhanced services needs of network operators worldwide. Current offerings include prepaid for 2G, 2.5G, 3G GSM mobile networks, number portability, mobile number portability, CLI screening, freephone, personal number, lawful interception, and INgate services gateway. For further information visit http://www.tango-tele.com

About Sonus Networks

Sonus Networks, Inc. is a leading provider of voice infrastructure products for the new public network. Sonus' solutions enable service providers to deploy an integrated network capable of carrying both voice and data traffic, and to deliver a range of innovative, new services. The Sonus Open Services Architecture^(TM) (OSA) and award-winning Packet Telephony suite cut the time-to-market for competitive new service products, allowing carriers and third-party developers to expand market share and build important new revenue streams. Its highly scalable products fully interoperate with and extend the life and utility of today's public network. Sonus embodies in its management and staff decades of experience in developing carrier-class voice, data and multimedia solutions for implementation in the world's largest networks. Sonus, founded in 1997, is headquartered in Westford, Massachusetts and has EMEA headquarters in Swindon, UK. 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' Annual Report on Form 10-K, dated March 28, 2001, 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 Company's ability to grow its customer base, dependence on new product offerings, market acceptance of its products, rapid technological and market change, integration risks relating to the acquisition of telecom technologies and manufacturing and sourcing risks. 

For information please contact:

Jon Ould
Sonus Networks
Product Marketing Director, EMEA
Phone +44 1793 601 428
Fax +44 1628 788 734
jould@sonusnet.com

Thaddeus Albers
Tango Telecom
Business Development Manager
Phone +353 61 503 108
Fax +353 61 338 065
thaddeus.albers@tango.ie