The other day I noticed an interesting ad in my latest issue of Windows IT Pro magazine: a free Windows IP PBX. It can work with a SIP-based VoIP service, or use a PSTN-to-VoIP gateway to interact with traditional phone lines. These gateways are usually relatively inexpensive; the PBX is the most expensive part of the bundle.
Naturally, I was immediately curious as to whether it would interoperate with Exchange 2007.
I've got the software and manual downloaded, and I'm in the process of sending off a query to 3CX to find out more details. I'll let you know what I find.