I bought an 16 gb iPhone in January at an Apple store in the US with the usual ATT contract. I'll be spending about half my time in Sydney for the rest of the year and I guess I naively thought I could just get on a Telstra (plan) in Australia, which is indeed no problem, and swap out my SIM card. When I did this though the phone didn't work. The Telstra guy said my iPhone was locked. Ok, so what are my options?