I have a jailbroken 3gs. Sometimes without any warning my iphone will stop receiving cell service. When Im in the middle of a known high quality of service my phone will not receive any bars. My phone still displays that Im on 3g service still but with no bars next to the carrier icon. I cannot send or receive text, call or receive calls, and do any internet surfing with this random problem occurs. It will only fix itself when I manually restart my Iphone. I was wondering if anyone has any ideas how to fix this problem.