I purchased the iPhone 6 a few weeks ago.I then decoded to go with a Moto X instead. I am trying to sell my iPhone now, but many potential buyers are asking if it is unlocked. I called AT&T to see if they can unlock it but they refuse (fwiw I have been a loyal customer with them and pay for a family plan for the last ten years). I asked the rep if I can still sell it but she claimed that no other SIM card would work in it. Is that true? If it is true, what does AT&T get out of this?