Will a T-Mobile sim card work with a At&T cell phone?

[Sedrick]

Can i put my tmobile sim card in a at&t phone and have it work properly? What would happen if i did this?

 

[tasteyy]

You need to Unlock the Phone from AT&T Network then use with other GSM Network Sim card....You can get the Unlock code from here unlock-free.com
and unlock it..Then use any GSM Network Sim card.