My girlfriend and I are on a Family Plan. I've got an iPhone 3GS, she's got a Samsung SGH-A877. She hates it and wishes she'd gotten an iPhone when she had the chance (obviously, we're out of the 30 day window, by a long shot). Now, her parents are out of contract and month-to-month with AT&T also. She'd like to add them to our Family Plan and obviously they'd be due to upgrade their phones. Her idea is to add them, have one of them get a 3GS (not the iPhone 4), and then she could put her sim card in the 3GS and use it instead of her parents (they're ok with this since they could care less about having an iPhone). My question is, would this work? Could my girlfriend just swap the sims and use the iPhone and would she still have her number or would she now have one of her parent's numbers? (As you can tell, I don't know much about this...lol).