[jibi]

UMA treats WiFi as simply an extension of the cellular network, like another tower. It hands off the transmission seamlessly to the WiFi network and back on to the cellular network and so on and so forth. This WiFi connection will connect you back to a GSM gateway on the T-Mobile network. Obviously, if the signal is not ideal, service will suffer (think of it as a wireless version of Vonage's VoIP product, except way more advanced (and way more buggy at this juncture) and the fact that you can leave your house, hop in your car, drive to Wal-Mart and pick up the wife some ingredients for supper, etc. and not drop a call you're on with your kid who's having anxiety withdrawals on their first day of college).