asterisk users - Jul 2003 - Large-scale voicemail deployment: any experiences?

Hello -
   I'm looking for a cross-section of your experiences for large-scale 
voicemail system deployment using Asterisk, where "large scale" means 
500 active users or more with PRI channel access.  I have a situation 
that may call for an extremely large stand-alone voicemail 
installation, and I while I have faith that Asterisk can handle 
almost any load if correctly designed, I'd appreciate your pointers 
so that I do not have to dig my way out the same pitfalls that you 
perhaps have already discovered.

   Of course, I am competing against large closed-source "box" 
vendors, and a success would be a major win for Open Source software. 
It would also very certainly get some press coverage due to the 
nature of the project, which I would expect would be a large boost 
for Asterisk's external credibility.

JT