Originally Posted by
Perche
It all depends on if you have a locked phone or not. If you have an iPhone and it's still under contract, you will not be able to avail yourself of any of this advice.
Not 100% true regarding the contract piece. If he's on a Verizon LTE iPhone (not sure if that's the 5/5S only), those ship SIM-unlocked. He could use that with any SIM, AFAIK.
If locked to AT&T, sometimes they will unlock for intl travel if you call, ask, get the right person and they're in a good mood.