When I go VoipPhone->ISP->ISP->Asterisk Box->ISP->Voip Provider->PSTN, I get intermittent jitter, BUT...the asterisk is running MixMonitor and the recording is always clear as a bell. The jitter is coming at either PSTN/VoipPhone end, or both.
I guess the fact the recording is always clear means its the downlink, but could be either side. Is this just a fact of life? (The asterisk is behind a fibre broadband connection)