This is a pretty basic question but I've never actually swapped phones before. We're both on the same AT&T plan, I'm upgrading to the 5S, but instead of selling my 5, I want to give it to her, and sell her 4S, since her phone is in better physical condition. What's the best way to go about doing this? I think the SIM sizes are different... appreciate the help, I know this is elementary stuff but I've never actually done it before. Thanks all.