I have both an ATT and Tmobile account and currently unlocked my iphone. I was debating about taking the iphone to tmobile when it occurred to me that when apple releases a 3g phone in the near future, having a tmobile account will be useless since the 3g iphone will not work with tmobile 3g frequencies. Therefor I have decided to stick with ATT and upgrade to the 3g phone when it arrives.