In addition, Sipera has partnered with AGN with an aim of securing SIP trunking, and the IPCS has tested interoperable with systems from Avaya and Nortel.

How it got its start: Founder and CTO Krishna Kurapati sold IPCell Technologies to Cisco for US$213 million in 2000, then pulled together a team of engineers to begin work on enterprise VoIP security out of a one-bedroom apartment in Dallas.

Management: The company has no CEO at the moment. Ben Scott, a venture partner from Austin Ventures, holds the chairman title. The name, Sipera, stands for the "era of SIP," referencing the popular VoIP protocol.

Funding: US$29.5 million from Austin Ventures, Duchossois Technology Partners, Sequoia Capital and Star Ventures.

Who uses the product: Goldsmith Agio Helms (a 2006 Enterprise All-Star Award winner), plus others

Interesting fact: Sipera has a development center in Hyderabad, India.

Tango Networks

Founded: October 2005

Headquarters: Richardson, Texas

What it offers: An appliance named Tango Abrazo that performs fixed-mobile convergence (FMC), linking almost any mobile phone with any enterprise voice system, whether legacy TDM or IP PBXs or hybrids. No client code is needed, nor a wireless LAN connection, not even VoIP, although Abrazo supports it.

Why we like it: A flock of start-ups and big players are getting involved in this move to fixed-mobile phone convergence. The Tango appliance makes full use of features on the PBX itself. Also, the company has no limitations on the type of phone (or PBX) supported, while some rivals require the use of smart phones that have a Wi-Fi adapter and VoIP. Cell phones are registered and provisioned on the appliances, which talk to each other during the call set-up phase using a Tango SIP-based protocol. The mobile phone becomes an extension on the PBX. Tango announced support for IP Multimedia Subsystem, important for emerging advanced carrier services. In August, Tango inked a deal with Strata8 Networks that will provide Tango's FMC service to the enterprise market in nine states. The service is slated for the first quarter of 2008 in selected cities of Florida, Indiana, Kentucky, Ohio, New Mexico, North Carolina, Texas, Virginia, Washington and the U.S. Virgin Islands.

How it got its start: Founder Andrew Silver says he could never figure out why he couldn't just connect his existing mobile phone to the corporate voice system already in place. So he created Tango to do that. As for the company name, Silver liked the word "abrazo," Spanish for "embrace," the opening move of the famous Tango dance that brings two partners together. In this case, the mobile network and the enterprise phone network are coming together.

Management: In October, COO Alastair Westgarth became CEO. Founder Doug Bartek, who had been CEO, will retain the chairman role. Founder Andrew Silver, an experienced wireless industry executive, is CTO.

Funding: US$25 million from Motorola Ventures, Nortel, Signature Capital, TWJ Capital and Meridian Capital.

Who uses the product: Abrazo is in trials with several Tier 1 mobile carriers and in beta tests at select enterprise sites. The company anticipates releasing enterprise customer references in early 2008.

Interesting fact: Although Silver came up with the company name to convey two things -- in this case, the mobile network and the enterprise phone network --coming together -- as in the opening moves of the tango -- he says he is not an exceptionally good dancer.