After an agonizing 4 days of over 75 failed calls and 3 system restores and 4 reregistering my iPhone 3G with the network and 4 times of resetting my network settings, Apple and AT&T have admitted that there MAY be a problem with my phone. I have an appt tomorrow at the Apple store where I have been told by Apple that they will exchange my phone for a 3GS model. Has anyone else experienced this?