This article on IP SLA monitoring may have just what you need.
You can also try this. This is a tool that will monitor your Internet connection 24x7x365 and give
you a MOS score between 1 (poor quality) and 5 (excellent quality). VoIP Spear monitors your latency, packet
loss, and jitter to calculate the MOS score.
Note that you can also have VoIP Spear send you email alerts when your VoIP quality drops too low.