I just ordered a 5s, from AT&T, to replace my 5. I used my wife's upgrade, because mine wasn't available for another year. Once the phone arrives, I want to put my line on the 5s, and put my wife's line on the 5 (which I'm giving to her to replace her 4s). Can I just switch the SIM from my 5 onto the 5s, and switch my wife's 4s SIM to the 5? Or do I need to go into AT&T and ask them to do something more than just SIM-switching? Thank you for the help.