@Almighty1: Thanks for the Wikipedia cite.
Most of my GV numbers seem to be working fine tonight. Interestingly, the one exception is a number that I access through the Simonics Google Voice Gateway. It shows as registered, but I get a busy signal or 503 error whenever I try to call out, and it rings to GV voicemail when I try to dial in.
Guess I'll check it tomorrow and see if anything has changed.