The problem with doing calculations with VoIP is that it shares it’s space with other data traffic. Traffic shaping is fundamental to the whole thing, as voice traffic should normally be given the highest priority thru the network. Blocking is not really the issue in an IP network, packet loss and delay are!
So what I would like to see is the abilty to calculate the bandwidth to provide a given CoS, during the Busy Hour, whereby say no more than x% of the packets are delayed more than y mS. Where the Busy Hour is based on both voice and data traffic.
If you need some useful source data, suggest that you talk to people like NetReality or RAD as they have products collecting realtime traffic data on VoIP now! networks now!