http://www.leonidsystems.com/publications/the-unofficial-voip-debug-cheat-sheet
http://www.cisco.com/c/en/us/support/docs/voice/voice-quality/7934-bwidth-consume.html
http://www.invoip.com/blog/bid/103477/How-many-calls-can-I-make-over-my-T1-with-hosted-voice