I thought someone would say something like that.
The system in concern is a Mitel 2006 model, which supports a maximum of 700 clients (SIP), and the system is currently running up to 650 mark. As far as I am aware this Proprietary system has little scope for expansion and is not feature rich.
But listen to this: The current owners started out with this system as a trial, they then decided to keep going with it as it seem to do what they wanted, the average cost of each device with licence and mailbox licence has set back around £200 per client.
I don't need to tell you that's around £130,000 of kit, or over there in the states 205,952.50 USD. That may turn out to be useless unless they again upgrade to a new Mitel system with upgraded licences so addtional costs after the purchase of the server. ouch. not bad for a not for profit organisation.
Let me know how you get on.