Hi all, I've been searching for a little while now for the answer to this question but have yet to find a clear answer. Apologies if it's already been answered! A member of my family will probably be getting an iPhone when the new version is released, but they have made it very clear that they wouldn't mind trading phones with me so that I can have the new one at no cost and they would use my current 3G. Gotta love family My question is, since we will be on separate AT&T plans (although they will both have iPhone data, etc.) can we simply switch out our SIM cards or do we need to somehow notify AT&T of the change?