I rarely use a cellphone, so haven't been able justify spending $70/month on an iphone. Currently I just use an AT&T "pay as you go" (prepaid) GoPhone, which costs me about $10/month. But I love the iPhone and really value internet connectivity everywhere so I've always really liked the idea of the non-existent data only iPhone plan. My girlfriend has a 3GS (with iOS 4.0) and can upgrade to the iPhone 4 for only the cost of the phone ($199-$299) + $18 upgrade fee. If she does this upgrade does she get to keep the 3GS? Assuming she gets to keep the 3GS, can I just put my sim card in it and use it as my prepaid phone? (the sim card does say 3G on it if it matters). Do I have to jailbreak or unlock it for this to work? Also, is there any way to get a working data plan as well? What are the plan options for this (I see an option for "Data 100MB" for $20 on my ATT account). Is this the best option for me? I would gladly pay $20-$30/month for a decent data plan. 100MB seems a bit small, though... Thanks!