Point to point and heavily used. I'm working now to QoS the PBX traffic, minimize the existing traffic on the links and some other queuing and stuff. I can affect all traffic except the PBX.

The confusing part is that the central location drops the most calls and the traffic to and from that location wouldn't touch the network.

Monitoring indicates that 3 out 4 of the locations not having problems are in the top 4 most congested links. Other than this (contradiction) there is no correlation between link usage and problem frequency.

If it IS disabled, then is it correct that the network won't be able to affect the voice packets? Have you had any success manipulating this traffic at layer 3 (IP)?

You've been fantastic help already. Thank you.