Well, AT&T is calling it game over on the VoIP game. I have been using CallVantage since 2004. It has worked very well with some pretty decent quality. It has an easy to use portal; call forwarding; simul ring; click-to-dial; voicemail-to-email; and more. Oh, yeah, the Simple Reach number so I can provide clients with a local number.
If you offer a similar service, start advertising to take over the 150K customers.