I bought a iPhone 3GS 16GB off a girl at work. It was a O2 contract phone, her contract was up and she got a new phone. The Sim card that is in it at the min is a tesco pay as you go from a old phone. Tesco Sims work on O2 network. The phone was fine for 2 days but now I have a problem. If the phone is plugged in to USB or charger it works fine, I can receive calls and texts. The phone does not have any credit on it because I was going to get a O2 simplicity Sim card. When its not connected to USB/charger the phone only works in Airplane mode, as soon as I switch airplane mode off the phone shuts down within a few mins. So for the phone to be truely mobile it has to be in airplane mode?! OK for pilots but not for peasants!