Robz75

I would recommend Nortel. One of the great things about the new 1000E is that each Media Gateway can be survivable in the event of a WAN outage. This pbx supports triple registration. If your main processor goes down all the phones and media gateways will register to the alternate CPU. If that CPU goes down then the IP phones and signaling servers register to their local media gateway.

Nortel Supports SIP, H.323, Integration with Microsoft Exchange 2007, and a PDA client so you can answer your desk phone from anywhere.

The 1000E supports 22500 IP ports (phones + IP trunks) and 5000 TDM Ports (Digital and analog phones as well as E1/PRI ports)

The 1000E supports up to 50 media gateways so you could have conservatively 200 PRI circuits if not more.

The 1000E is built on the VXworks platform which has been rock solid for years. NASA used VxWorks to run the Mars Rovers.