Say I purchase an iPhone and use iPhone plan, but I also purchase a second phone, like a RAZR from AT&T, can I switch between phones via switching the SIM card from one device to the other? I have always been a CDMA customer (Verizon and Sprint) so I've never had the ability to use SIM Cards. I would like to purchase the iPhone but have a secondary "backup" phone as well. Also -- Same question but instead of the iPhone and iPhone plan and a RAZR (backup phone), but a BlackBerry Curve and a BB plan and a backup phone. Can I just take the SIM and switch phones? Sorry for the newbie questions.