He fiddled with things, ran some diagnostics, was unable to get a signal through, then hung on hold to the mother company for about 40 minutes.
He was apparently a house technician, and needed a street cabling tech to come out and find out what was wrong further down the pipe. That guy was supposed to show up tomorrow by 6:00.
Shortly after he left, I started getting a response on my firewall, though it took until I thought to reboot the firewall before the rest of the house network came up (D'Oh!).
I have no idea if they fixed something remarkably rapidly, or if the SBC guy removed enough grunge from the contacts to get a signal through, but either way, it works now.
Yay! I can feed my addictions at high speed again!