I'm looking for a good website dressing a comparative analysis of the most popular telephony solutions resellers (Cisco, Avaya, Siemens, Microsoft, etc...). I already found a very nice work comparing Cisco and Avaya, but it's not all. What is interesting for me are the performances, the evolutivity, all the technical data, the size of the hardware for a few different configurations, etc. Thanks for your help.
SnapOverflow
There is a ton of information here:
http://www.voip-info.org/
It's mostly related to the open source solutions so it may not be what you're looking fo but there is still a good amount of info. Especially on the phones themselves.