Voice Quality Monitoring Software Solution

I have a couple of larger (250+ phone) Asterisk installations - both installed and in planning. I've seen a couple opportunities for open source VoIP that would far exceed that number.

Commercial closed-source end to end offerings often seem to include a quality monitoring tool (Cisco Service Monitor, MS Quality of Experience, etc..) or people tack on a Prognosis or Edgemark style solution. I would like to be able to come up with a lower cost voice quality monitoring solution that reaches this level of sophistication.

I am looking for something capable of MOS, loss, jitter, delay, etc... and a graphical representation of quality.

I have found one open-source project that meets some of these requirements - called ntop (http://www.ntop.org/overview.html). Other than that, I'm not sure if anything more than simple SNMP / Nagios style monitoring exists.

Has anyone done this? How has it worked, and what solutions have been used? If this is a perceived hole in the solution stack, is anyone else interested in looking at what it would take to develop a software-based solution for this?

Thanks,

Josh