SO I was wondering if I can buy an iphone off craigslist or off a friend and still use my current SIM card in it? I'm currently on AT&T and my friend lent me use his old iphone when we hung out once and i put my SIM card in it and it worked fine. His wasn't even unlocked or anything. If i ended up doing this would I still be charged my same old phone bill? OR would I be charged the an iphone styled bill? (30 dollar data plan, 20 dollar texting etc). Also would it make a difference if i got an unlocked iphone as far as my bill goes? I really want an iphone, I just don't have enough to pay THAT MUCH monthly if i signed for a 2 year plan you know haha. Thanks!! An answer asap would be awesome! 