So I am almost at the point of pulling the trigger on an new iphone with att, but I had a question. Since it such an expense phone, I wouldn't want to take it to the beach, boating, snow skiing, etc. I am used to CDMA carriers with no SIM cards. With GSM SIM cards can I just buy an unlocked GSM phone, say the motorola V3xx, from ebay, and just swtich the SIM from the Iphone to the V3xx whenever I want and it will work flawlessly?? That seems pretty awesome.