Anyone here (in the US) owns a factory unlocked phone? I'm asking my Canadian friend to buy one for me. Are there any problems you have when using it with T-Mobile or other carriers? I'm actually an ATT subscriber, but I won't be staying the US for long, so I'm gonna need the factory unlocked kind. I do not wish to cut up my SIM card... Do you think I can just go to the apple store and ask them to switch it to a micro-sim card?