AT&T has been recently forced to unlock their GSM phones at the customer's request 90 days after the phone purchase. Exceptions are the iPhone and for phones under an "exclusivity" agreement which would last no longer than 10 months. Prepaid phones can be unlocked after you provide a receipt for the phone's purchase. We're not trying to use our AT&T phones on other US networks, we're trying to use them internationally by inserting a local SIM. Some phones are easy to unlock, but yours seems to always be the one that isn't.
We compared AT&T's "new" unlocking policy with other GSM carriers. T-Mobile will unlock your phone for you after 40 days with postpaid accounts and 6 months for prepaid. The next largest GSM carrier, Cincinnati Bell Wireless, won't unlock phones under any circumstances. Our favorite GSM carrier, Viaero Wireless, doesn't have a lock on their phones, except for certain Blackberries.
The only reason the courts forced AT&T to provide the unlock codes is that they were accused of being 'misleading' in providing locking information to their customers. We found that AT&T would provide the unlock code after a 2-year contract was completed, or if you could convince them you would be roaming outside the country and would need to insert a local SIM.
It's unfortunate that it takes a court order to make the wireless companies be more consumer-friendly. AT&T needs to learn that some of their customers are lawyers and they should be treated nice or they'll do what lawyers do. For once, that's a good thing.