Quick question. I'm one of the people who have a 3G phone and I'm not eligible for the upgrade. My girlfriend would like an iPhone, but the regular 3G is fine with her. If she switches to AT&T as a new customer and I buy the 3GS for her, will we be able to swap sim cards so that I can use the 3GS and she can use my 3G? Or is there more to it than that? Is the phone itself tied to your account?