Mobile VoIP technology is marching forward. WiFi telephones and walkie-talkie-like communicators have been used in hospitals and offices for a while, but now manufacturers and mobile carriers are getting ready to link cellular networks to the myriad WiFi hotspots dotting urban landscapes. This linking will expand coverage and make for cheaper mobile minutes. The technology used for such linking is unlicensed mobile access, or UMA. UMA transmits cellular information packets through the Internet when WiFi is available, but reverts to cellular towers when WiFi is not available. A back-end controller inside the network makes the switch--ideally, without the user even realizing it. The technology will help those with high-speed WiFi routers compensate for poor coverage in their houses or apartments. It will also allow mobile carriers to expand their area of coverage without investing billions on new infrastructure. For users with souped-up handsets, UMA would allow wireless downloading of content at broadband speeds.

ABI Research expects the market for WiFi-enabled mobile handsets to reach 100 million units annually by 2009. European carriers have shown distinct interest in UMA: France Telecom will be the first European customer for Nokia's UMA phones, and TeliaSonera is moving ahead with trials for business customers. U.S. carriers have been more circumspect, even as representatives of Nokia and Samsung say they would start selling functioning handsets in the U.S. this year.

UMA poses a problem for operators. Cingular, for example, may be concerned that offering WiFi calls inside a home might nibble away at the land-line business of its parent companies, AT&T and BellSouth. On the other hand, UMA would allow traditional land-line phone companies to retain customers who are increasingly using VoIP phones. Steven Shaw, director of marketing for Kineto Wireless, a Milpitas, CA-based company developing UMA technology, is blunt: "This is a proactive response from them to get out of this threat of voice over IP... You see this giant bucket of minutes called fixed-network minutes going toward zero because of Skype and voice over IP," he said. "You've now got the option to take those minutes and put those on the mobile network as fast as possible. That's what UMA does."

For more on the move toward UMA:
- see Carmen Nobel's Unstrung report
- and Ryan Nakashima's Rocky Mountain News analysis

PLUS: Trapeze Networks claims that earlier this week it became the first WLAN infrastructure provider to demonstrate seamless mobility between a WiFi and cellular network. Trapeze teamed up with DiVitas Networks, a provider of unified mobility solutions, to demonstrate interoperability between each company's wireless platforms over any dual-mode handset that supports Windows Mobile 05. Release

ALSO: Is WiFi roaming really seamless? It depends. Tutorial

FINALLY: The Bull Market Report, an online investment newsletter, is offering subscribers a report on companies likely to benefit from WiMAX, including Alvarion, ADC Telecommunications, Airspan Networks, Vyyo and others. Site