My iPhone 4 no longer has 3g network. I am running AT&T, and I can make phone calls and send text messages but I cannot get internet. When I run Safari or any other web based application I get the "Could not activate cellular data network" message. My iPhone was once jail broken but no longer is. In the corner there is no 3g symbol next to AT&T. I have tried resetting data settings and restoring it but nothing works. Please help...