I'll be selling my new 3GS (hopefully for $400) and buying a iPhone 4. When I did this with the 3G to 3GS, I just swapped SIM cards in the iPhone at an AT&T store. With the iPhone 4 using a smaller SIM card, how is that going to work? Hopefully I'll sell my iPhone 3GS this week and then I'll be waiting for a couple of weeks for the iPhone 4.