T-Mobile has become the first major carrier to allow a phone in the U.S. to communicate over both cellular networks and WiFi hot spots. The NYT has a good summary of the significance of this step, which is considerable.

Keith Higgins, who works for Stoke, wrote at VentureBeat about the possibilities of this sort of service last month.

Clearly, this could hurt a lot of Internet telephony companies, like Vonage and the plethora of other start-ups in this area. You can bypass them now by simply making a call with your cellphone, using your home WiFi connection (if you have one, of course). T-Mobile is behind in terms of customer count, and so this might help them. However, other carriers are bringing similar offerings to market soon.

More details are here.

From the Times:

The first phones, which are available to consumers in Seattle on a trial basis, link to T-Mobile’s cellular network outdoors and to Wi-Fi routers at homes, in offices and in other locations like airports and hotels. This lets customers avoid using some of their cellular minutes and increases coverage in places where signals are typically weak, like basements and rooms without windows.

To gain access to the service, called T-Mobile HotSpot @Home, customers must buy a phone that works on both networks. T-Mobile is selling a choice of two handsets that cost $49.99 for customers who sign up for a two-year rate plan for at least $39.99 a month. Subscribers are charged $19.99 a month in addition to their regular cellular plan fees.