I have an iPhone 4 and my significant other has an iPhone 3G. They just bought an iPhone 4S and is willing to trade it for my iPhone 4. My phone is already registered under my name and all, while the new iPhone 4S isn't registered under anyone's name yet. What is the best way to go about transferring all our data correctly? Do we need to go to our cell carrier or to Apple?
If it doesn't work out you can just restore your phone from the latest backup.