yes u can u need an unlock code my sister found this website i dunno if its legal or not but they unlocked the phone for 20 bucks. we had t mobile and her phone was at$t though
No you can't use AT&T sim in the phone which is already locked with t-mobile until you unlock it ...You can easily unlock your phone through online providers like WickedUnlock.com here they are rendering network unlock code for all mobile models at reliable cost .You first check that whether the code is available for your mobile model ,country and network provider .If yes then pay for it and unlock your phone then freely use it with any GSM sim ....