reply to Mango
Re: Out of curiosity... Both CallCentric and Anveo offer hunt groups with Answer Confirmation, as well as inbound and outbound FAX. Anveo offers SMS (CallCentric does not).
VoIP.ms has been promising FAX and Answer Confirmation for close to a year now, with constant commitments that these features would be coming "soon."
As far as the rest of the features are concerned . . . the ones that are important to me are offered by all three vendors and many more. My initial attraction to VoIP.ms was its support for Ring Groups, as I have both a home and vacation property that I split my time between. However, adding a cell phone to such a ring group without call confirmation significantly impairs that functionality.
The one fundamental advantage that VoIP.ms has is in toll-free/8xx outbound calling . . . it's free and is the most significant reason I have not switched to another service.