Yes, I found that forum topic right after your first post. Thank you gderf.
I guess I was wondering if Google had rolled out a recent update that was causing this problem, but that doesn't seem to be the reason based on the fact that people were having this problem while I wasn't. Of course, Google doesn't always do a blanket rollout to its servers, but since my phone is now ringing again, it doesn't appear that the update theory holds water.
Anyway, if any of you are still using the GV/CC setup and your phone stops ringing, try deleting and resubmitting your CC number to GV.
UPDATE: Right after I wrote this, the phone rang one time. I tested it with my cell phone and, sure enough, it's ringing on my cell phone, but doesn't ring on my OBi-connected phone until the last ring. Same problem as right before it stopped ringing completely.
So... MY SOLUTION DOES NOT WORK.