You can genrally assume for most businesses in the developed world which use a key system or a PBX, that the average duration of a local call is about 3.5 minutes and the average duration of a toll ( long distance) call is about 2.8 minutes. The ratio of local to toll calls is about 5 or 6 to 1. And the average traffic in the Busy Hour is 4 or 5 CCS ( 0.11 to 0.13 E). Call centre traffic does not have this characteristic though.