I bought a 1st gen iPhone from a guy off craigslist. He got it the first day it came out, so the warranty is no longer good. AppleCare wasn't purchased for it and it is too late to purchase it. Once every day it suddenly says No Sim and I take it out, put it back in, power on and off, and it starts to work again. This happens every day. Another problem, I will stand in one spot and about every hour or so it will lose signal for 15 minutes, but I haven't moved. It goes from full bars to no service. Any ideas as to what I could do? Would Apple Store exchange it for a new one?