re: How to transfer old iPhone to someone else?

If you have enough sim cards that fit in your new phone and your old 5, all it takes is an activiation call to AT&T. They will deactivate her old phone, activate your old sim card/phone on her account after you have deactivated your 5 and activated your new phone.

Or you can just go to an AT&T store like already suggested and they will do it.