This seems like it should be straightforward. My iPhone 4 touchscreen is dead. While it gets repaired/replaced, I'd like to use my old iPhone 3GS, which has been reset to factory settings, cleared of all data, and is basically in an as-new state. Having upgraded iPhones 3 times now, my experience tells me that restoring from backup should set up the 3GS as a new phone, activating it and transferring everything over. It has always been painless. This time, however, while data, apps, settings, etc. are all copied over, the phone is not activated and I don't get any service. Is there something about reverting to an older model that prevents iTunes from treating my 3GS as a new phone? This is crazy annoying.