iPhone 5 carrier question ( AT&T and Verizon )

No such thing. Completely different systems. Verizon does not have sim cards.

Unless of course you had a Verizon phone that was approved for international use as the non North America world uses GSM because Europe mandated it. But since you are going the other way there is no way that it is going to happen. You can sell that thing on Ebay in five minutes for more than you will pay for a new Iphone 5 with a two year contract when you switch.