Can an AT &T phone be used by another carrier, Ie T-Mobile? And how do you do this?

[sticks_hawk]

Can an AT &T phone be used by another carrier, Ie T-Mobile? And how do you do this?

For Example: I have a Motorola Razor and want to give it my Daughter, but her mom has T-Mobile, I use At&T.. What Do I need to do to allow her to use the phone, with thier account.

 

[Unregistered]

If you want to make AT&T phone to use another carrier like T-Mobile means,your phone should be unlocked one
If it's network locked phone means,you will need to unlock it.For unlocking you can approach your service provider or else try to buy an unlocking service from any one of the online unlocking service provider like Unlock-Zone.com