This is good if you're actually currently an AT&T subscriber, and as long as you haven't done it within the last 90 days or something like that.
Basically, if you try to unlock a bunch of handsets for a family trip, you're outta luck. Even more so if you're no longer on AT&T!
Depending on the handset, there are actually some really easy ways to do it online for free- if you look in the right places. I've unlocked many gsm phones, regardless of provider, and even if I wasn't a subscriber of any of the gsm networks!