Microsoft announced a new server version – Windows Server 2008 Foundation. In a nutshell this is a lower cost OEM version of Windows Server 2008 – of course a few features have been removed but all the key features are there including Active Directory. Essentially a File, Print (and why not PBX) server for Small to Medium business.
With server costs as low and hardware specs as good as they are today, the average brand new rack mounted $1000-$1500 server will easily be able to handle being a PBX as well as a file and print server.
And if such a server runs Windows Server already, pre-installed just like the way you buy a notebook, then choosing a Windows based PBX as your next communications solution is pretty much a no brainer. :-)