My son will be attending medical school on the island of St. Maartin for 2 years. The school campus is full-time wifi. Our USA carrier is AT&T. We have been advised by current students to drop his AT&T service just before departing, and bring an unlocked GSM phone and an unlocked smart phone to the island. Purchase a local calling card for the GSM phone for local calls. Get a USA local number and GV account while in USA, then install GV app on the unlocked Iphone and on your island computer for calling back to the USA, I am assuming, via wifi. Does this make complete since to anyone as the most economical method for phone service while there?

Here are the points I am confused on:
1. Do I put any type of phone card in the unlocked, non AT&T Iphone?
2. If I dial the GV number from the USA, and my son is in a wifi zone, will his Iphone ring?
3. If in a wifi zone, will my son be able to dial the USA and speak to us, at the affordable GV minute rate?
4. If out of a wifi zone, can the USA based call be forwarded to his GSM island phone and not be charged international rates on the local calling card?
5. Is someone willing to explain, in detail, how to configure the unlocked Iphone and GV now to simulate the above while still here in the USA?

Thanks,

Bill