how do i make a tmobile phone use a at&t sim card?

[totsey]

i have the blackberry pearl and i only bought the phone so im not on a yearly plan for it so i got a new phone and im giving it to my boyfriend and he has at&t so i wanted to know how to be able to use that or if its possible?

 

[tasteyy]

If you need to use the AT&T Sim card in the T-mobile Phone means you have to unlock the phone from network lock.you can use the unlock code to Unlock it.You can get the unlock code from the site Unlocking4u.com and unlock it easily.Then use with any GSM Network Sim card.