3GS intermittently receiving calls/voicemails, delays sending/recv'ng texts

This just started today: I would suddenly have two or three voicemails in my inbox, and my phone didn't ring. Then I started having problems sending and receiving texts--weird delays, failed sends... Suddenly three old texts arrive at once. And problems calling out--takes anywhere from three or more tries to successfully make a call.

I restarted the phone, have synced it, switched to aiplane mode and back... nothing. It keeps working ok, and then choking. Intermittent problems are the WORST.

Argh! Is this an AT&T thing?

Ideas?