Interesting story on T-Mobile launching a WiFi VoIP and cellular service next month:

T-Mobile plans to launch a Wi-Fi-cellular converged phone service in Seattle and potentially one other market next month on September 12th, sources say. More markets will follow soon after. The city of Chicago and the San Francisco Bay Area are the likely candidates for a possible rollout.

T-Mobile’s converged service is based on a standard called Unlicensed Mobile Access, popularly known by its acronym, UMA. The news that T-Mobile has been doing trials of services using the wireless convergence standard UMA have been slowly coming to light. Business Week points out a service targeted at in-home cell phone users called T-Mobile-At-Home, which seems like UMA, but the article doesn’t name the standard. Engadget had also posted information about the UMA trial.

We’ll see if T-Mobile can meet its planned launch date, but the company is eager to start deploying UMA given it can not only take a piece of in-home calls, but can also use UMA to handoff in its thousands of T-Mobile WiFi hotspots. UMA is a standard that enables the handoff of calls between cellular (GSM only) and unlicensed wireless like WiFi.

More than any other carrier in the U.S. T-Mobile has the incentive to use UMA — it ranks behind the top 3 U.S. carriers, only reported 613,000 net new customers for the second quarter of this year, and owns valuable WiFi real estate that it can use to grow those subscribers. The company would only confirm that UMA is one of the technologies that the company believes will help replace landline calls.