Are there hardware differences between the ATT and Verizon iphones? Or is it just the sim card? I just realized that my aunt might have an upgrade available on her account (which she will let me use), the only problem is she is ATT and I am on Verizon. Can I just use her ATT upgrade and get a Verizon phone? If I get an ATT phone, can I just put in a Verizon SIM?