Hmmm, new virtual PBX? Saw this posting to the VoIP Forums this weekend claiming to be a new virtual PBX which they term VPBX. Why not call it "hosted IP-PBX" like most people? Anyway, the posting was here:
New VPBX Product : Forums
Talkisp (http://www.talkisp.com) has a product called Unimessaging (http://www.unimessaging.net) that is a full featured VPBX. It includes conferencing, Caller ID, Unlimited Voicemail, Call waiting, and much more for only $35.00 per month. This ACD system is built on SIP and can unite multiple locations with only one PBX. It allows trunking to call centers and can tie analog lines into the VPBX. A fine product I found out and is very cost effective. I highly recommend it.
I'll have to look into this a bit more, but it looks like they are targetting ISPs to resell this service and they leverage SIP.