I have a better idea
I have a better idea. If you have Android, get an app called GrooVe IP, or, if you have an iPhone, get an app called Talkatone, set them up with a Google Voice account, and make VoIP calls at Google Voice rates, which I'm sure are going to be lower than what AT&T charges. And, since calls from your Google Voice number to other U.S. numbers are free, you won't have to pay to call back home when you're overseas.
International roaming charges are based on what network you're using when you make/receive a call, not what number you called. If you making a call while roaming overseas, you will pay international roaming charges.