Note, I've done some research into the subject and I am only looking to clarify a few details. Now, let's say that I buy a used iPhone 4S that is locked to AT&T and restore the firmware. I know that software unlocks don't exist, so can I just buy any old AT&T SIM card to activate it and use it as a camera/PDA without any data/voice plans? Also, if I elect to buy a factory-unlocked 4S straight from Apple, will I need a SIM card to activate it and use it? Thank you.