One day, for not reason, my 8 month old 16gb iphone 3G could not place an out going call. I backed up the phone, then restarted the phone, rebooted the phone, reloaded the OS onto the phone... so I finally when to the Apple store and they did some testing and reloading themselves, to no avail. So they gave me a new phone. Problem fixed. Bravo Apple. Bravo Apple support!