Wirelessly posted

If I buy an AT&T 8820 and I use it on the T-mobile network, will I be able to use wifi, GPS and UMA? Phonescoop.com says that the AT&T 8820 is capable of UMA if the carrier supports it, but I have heard that it is not capable of UMA. Can you guys please give me the correct answer as I am going to buy this soon. I need and want all three, GPS, wifi AND UMA.