True, I have those ports forwarded, but still get fast busy intermittently. My VOIPo VM is turned off, because GV forwards to my VOIPo number. During the past week, I'd get GV SMS/email VM notification while my VOIPo phone never rang. I would immediately check by calling my VOIPo number from my cell and get the fast busy.

It's hard to file a ticket on this, because no call log shows up, and the problem is intermittent.