Scratch that last entry - looks like my phone has been brought back from the dead!
When I went to the Cingular store in Mira Mesa where I bought my phone they did a cursory once-over but couldn't find anything wrong, and suggested (of course) buying a new phone. I asked if I could get it serviced and they said they didn't do it there but referenced me to PCS Connection which is a Nokia service center. So after work today I took it over, just to see what was wrong with it.
Well don't you know they got it working!
The VERY nice guy (whose name I didn't get - tall Filipino guy with a scar on his right cheek) took it apart and cleaned it (with a freakin' toothbrush no less), and the little fucker started right up. And he didn't even charge me! (I was going to buy another cover for my ear bud but they didn't have any.)
So let me recommend:
9932 Mercy Road (at the 15)
San Diego, CA 92111
They're a T-Mobile store, but they also retail for Cingular. They rock!