So my girlfriend is due for a full upgrade now through AT&T and I'm wondering if it would be possible for her to get the new iPhone with her upgrade when it comes out and give it to me and then I give her my 3gs. What would we have to do to keep our phone numbers? Would we just have to switch sim cards or would we have to go to the Apple store or AT&T store and have them do something? Or do they not even let you do something like this? I'm not very knowledgeable about how the whole cell phone stuff works.