The Cisco AVVID solution, utilizing the MCS7835 Server with Call Manager 3.0, can scale up to 100,000 users (and more)through the use of clustering. One MCS7835 Server can accomodate roughly 1000 users.
Add to that the Unity Messaging system (Unified Voice messaging) and you have a complete package, capable of handling Voice, Video and Data quite readily.
Having spent the last 3 months researching this, I am about to put a small VoIP “test network” in place here at my place of employment, to gather real-time statistics in preparation for a FULL-Scale deployment in Q3 of 2002.
Senior Network Engineer