Hi
if u hv 2 options to have the utilisation of u r PRI which is being used for VOIP .
1.Use Freeware MRTG S/Ws and pull out the necessary info.Graph them out in ur server.
2.Run NBAR in your router and get the necessary info related to voip ports.
second one is CPU extensive so do take necessary precautions b4 doing tht.
regds
prem