So I gave my iPhone 4 to my Sister when I upgraded to the 4S, but when she set it up with her carrier (Rogers, I was with Telus), the iPhone 4 could not recognize her SIM card. To my understanding, iPhones bought from the Apple Store are all unlocked. Can carriers lock these unlocked iPhones once you hook it up with them? If so, can they revert it back to being unlocked? I also read on another forum, that the Genius Bar can actually make it so that the iPhone, when plugged into iTunes, can recognize the new SIM card from a different carrier. Can anyone confirm or shed some light on this? Thanks.