Someone I know has a 4 & 4s, the 4 isnt in use. I asked her if she was wanting to sell the 4, and to my surprise she said, "yes, $100".... I immediately agreed, but with the fear this might not work out as planned. I say this because I am with T-Mobile. I know iPhones can be used on T-Mobiles network, but at what cost? Will she have to obtain the unlock code for the 4 from AT&T, or is jailbreaking the way to go.... Thank you for any responses.