Well, there's some data here that isn't entirely perfect.

Your best bet, I think, is to have them log the exact time of issues (disconnects, bad voice quality, whatever). When you get a chance, go back to PingPlotter at these times and look for latency or packet loss. If you find data in PingPlotter that looks supportive of the problem (2 in a row lost packets or > 100ms of latency), then you can look back at the earlier hops to see the first hop with problems.