I have a very strange voice quality problem. We have a remote worker who has 7941 phone plugged to a C851W SOHO router, C851W is configured as ezvpn client, the 7941 phone registers to CUCM in HQ, HQ has a 2821 MGCP gateway conncts to PSTN provider. When this employee makes calls to internal extensions, the voice quality was perfect, but when he calls external numbers (or external number calls in), the voice quality was bad. We don't have a whole lot of internal extentions, so all IP phones in HQ and the MGCP gateway are in the same subnet. IP connectivity wise, there is no difference between the audio stream of this remote 7941 <--> HQ hard IP phones and the audio stream of this remote 7941 <--->HQ MGCP gateway. We know the problem is not on PSTN side or MGCP gateway, because we don't have voice quality problem when making/receiving external calls from HQ hard IP phones. I can not think where to start the troubleshooting that makes sense.