I need some help. I want to sell my iPhone 3G and purchase an iPhone 3GS while keeping the same number, and preferably all my contacts and data. Do I have to unlock the 3G before selling it? Do I have to swap out the SIM cards? Can I still unlock the 3G after activating my 3GS? What happens to old iPhones after a new one is activated for the same AT&T account? Is there any way to sell back an old iPhone to AT&T/Apple? I would appreciate help in figuring out what process I need to follow to do this. I am sure many other people on this forum will benefit from this thread as well.