Hey everyone. I couldn't find an answer to this in the forums. I will be receiving my iPhone 5 this friday and my wife will be getting hers mid October. She is using a 3GS and I have a 4. (Both AT&T). I want to give her my iPhone 4 until she gets her 5. Could I just put her SIM card into the 4 and that's it or do I need to call AT&T to change it over for the few weeks she will have it? I appreciate the help in advance.