I have an ziphone unlocked, jailbroken, 1.1.4 iPhone with an AT&T contract.
I've had no problems but this morning I woke up to find "No Service" across the top of the screen. Wifi works and when I use *3001#12345#*, I can see 5-8 towers with decent signal. All calls fail except for 911 which I ended before it connected for obvious reasons.
Any ideas? Is this what happens if you don't pay your bills promptly?