My wife and I both have an iPhone 4 on the same account, but only her phone had an upgrade option. I pre-ordered the 4S, using her upgrade, but want to use it to replace my phone. Do I simply change the SIM from my old 4 to the new 4S, call AT&T to ask them to move service onto the 4S, or do I physically have to go into an AT&T store/kiosk to move my phone number to the new phone? Also, will any of these options affect desktop syncing? Thanks for your help!