you got it from the ATT site and the carrier is t-mo?? because the "8310" is att exclusive in the USA. t-mo has the "8320"
first lets confirm which it is...
on your connections manager, see if there is an option for "Wi-Fi". also, look on the body of the device itself. it should have a carrier branding on the body.
if it has Wi-fi, its tmo's 8320. if not, its more than likely the 8310. if you bought it from att, there is no way it can be the 8320 though. so im really confused... post back ur findings