Hello Gabriel,
The Hebrew University of Jerusalem has 5 old Nortel exhcnages serving around 8,000 extensions. For about 3 years now we have a FreeSWITCH PBX connected aside it with about 200 extensions (we do not put more extensions due to potential problems it might create on the Nortel).
We started with Asterisk and quite quickly understood that it lacks some functionality that an organization like us needs, thus we moved to Freeswitch, and we are happy with this decision. We also have AudioCodes ATAs for analog phones and AudioCodes PRI gateway. Our "smartphones" are mainly Polycoms for secretaries and AudioCodes HD320 for "regular" users.
We have to do some move soon as our Nortels are almost 20 years old. We are now in the process of estimating how much an open source solution would cost us (needs more man power which we have to estimate the amount of) so we can compare it to a commecrical solution offerings.
If you need more information don't hesitate to ask.
Regards, __Yehavi: