ATT will do it for all of their phones except the iPhone.if you have a 3G and you've had it a year or so, you should call ATT and ask them to unlock it because you are traveling over-seas. They did it with my RAZR v3XX.
What is the unlock code for my iPhone?: "iPhone cannot be unlocked, even if you are out of contract."
(Of course they really mean "it can be, but we aren't going to do it so stop asking!")