[silverado04]

Would a SIM card from an AT&T service work on a T-Mobile phone?

[subhashis_biswas]

absolutely it will work, if you have that T-mobile phone unlocked.I am using my ATT card on T mobile nokia 6800 phone for last 2 years almost, without any problem. But get the T mobile phone unlocked.If you are out of contract from tmobile, they wont do it. In that case , google " your phone model unlocked", and u will comeup with instructions from any discussion forums.