Has anyone had any problems with the iPhone 3G not taking calls? Friends have told me that they tried to call me but the phone didn't ring at all and there's no record in Recent Calls. I actually tried calling my phone from a landline and the same thing has happened. This has happened several times. It usually starts working again if I make an outgoing phonecall or reboot. I've only had my phone for about 1 month. Any ideas? Thanks.