Can I use a T-Mobile phone with AT&T service?

[JustSwim208]

I remember I got a motorola razr that was from the T-Mobile box and have AT&T service. Would I have to buy an unlocked T-Mobile phone to use it with AT&T?

 

[tasteyy]

If you buy an Unlocked Phone means you can use with any GSM Network Sim card.Unlocked Phones are costly than Locked One.So better buy a locked Phone and unlock it .You have to Unlock the Motorola Phone from the network lock to use other GSM Network Sim card like AT&T sim card..You can get the Unlock code from the site Onlinegsmunlock.com and unlock it easily.