[tsac]

Some carriers selectively offer UMA service depending on the location and service availability. T-Mobile and ATT both offer service but generally it is not to allow free phone calls. ATT offers a xxx8220;Femtoxxx8221; cell service that connects to your DSL service to allow you to xxx8220;forwardxxx8221; calls over WIFI but this service is not free also. Doing some reading I found T-Mobile does offer the service but it is generally not available without a plan and I suspect it is also limited to selective areas. T-mobile may have stopped the service in your area

Hope this helps

This is what UMA is supposed to be,
Unlicensed Mobile Access (UMA) provides access to cellular mobile voice and data services over unlicensed spectrum technologies, such as Bluetooth or Wi-Fi (802.11).

A UMA phone will use a cellular networks (GSM, CDMA, etc.) when out and about, and automatically switch to a UMA-enabled Bluetooth or Wi-Fi local network when in range, such as at home or in the office.

In local mode, a complete, virtual GSM or CDMA connection is "tunneled" to the carrier via the Bluetooth or Wi-Fi connection and the Internet. This allows seamless, transparent use of all services at all times, including voice, messaging, and data services.

This hybrid approach allows fulls mobility, while offering consumers better coverage, faster data rates, and lower service costs when using the local network.

The technology can also lower infrastructure costs for carriers, by reducing load on networks in densely populated areas, and reducing the need for towers in sparsely-populated residential areas.