What if I buy a 3G iPad in the U.S. for the UK? I know they're not locked, but when in the UK how would it work? As far as I know you go the settings app and can purchase a 30 day data plan from AT&T. How would that work in the UK? Would it know I was in the UK and show UK providers instead? And what about if I were to buy one in the UK and go to the U.S.?