HELLFIRE, experience has no substitute -- Inexperience carries significant cost and risk. I've forgotten how many botched up installations I've had to redo based on Telco geezers believing that they follow specs to the letter and refuse to adapt to reality.
With VoIP I've
leaned that 80Kbps full duplex does not cut it --- 128Kbps full duplex works very nicely each and every time especially under load of concurrent usage.