Network World did a face off on the subject of IP PBX’s and Hosted VoIP.
It’s a subject that will likely be one that is front and center as more PSTN PBX’s start to be replaced. The difference is really updates, features and applications, as well as one key differentiator in my mind. The cost of labor to maintain, update and fix.
With hosted you get all the updates and someone else does the maintainence. As this battle gears up expect the war of words to get mindshare to ever increase beyond the world of IP telephony and into the mainstream media.