Hi, 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 $25 every 3 months (to add minutes). But I love the iPhone and really value internet connectivity everywhere so I've always lusted after the idea of the 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. I'm assuming if she does this she'll be able to keep her old 3GS. Can I just put my sim card in her old 3GS 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? In my Go Phone account I see an option for "Data 100MB" for $20. 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... What exactly are my options here? Thanks!