I have a 3g iphone but not eligible (like most) for the subsidized price. I was planning to give my current iphone to my wife and purchase a 3GS. She is not currently on ATT. Would it be pretty straight forward to add her as a new line, get the subsidized 3GS on her line, and then swap the sim cards so I can have the 3GS on my line? What else would be involved with this?