Several sites associated with my employer have used vonage. As Hal said, it is hit or miss.
When my lab was in Waltham, MA, my vonage line worked _perfectly_. I've since moved to Portland, OR. At home we have a vonage line that again works perfectly. However the line that I set up in my new lab worked terribly. An associate who set vonage up at home in Baltimore, MD had no luck at all. But then they moved the box over into a lab space, and it seems to be working just fine.
We did discover a bug in the box that they provided. Vonage provides a box that works as both the VOIP interface and as a router. The idea is that you connect the VOIP box to your cable/dsl/internet box, and then connect all of your computers to the VOIP box. This is supposed to let the VOIP box do 'Quality of Service' control and make sure that the voice channel gets enough bandwidth. Essentially you are supposed to be able to pick up the phone, and the box will slow down all of your other downloads and make sure that the voice traffic goes through.
Well it turns out that the QOS feature has a bug, and when it is on the box spends so much time processing packets that voice quality just falls apart. If you turn off the QOS feature, then voice quality improves dramatically. The very feature that is supposed to protect the VOIP traffic kills it. With the QOS feature off in my Portland lab, vonage is again acceptable.
There is also an important failure mode that anyone using vonage for business needs to know about: you don't have any indication of outgoing line quality. You can have a _perfectly clear_ channel for listening, but the person on the other end of the line can't hear you speak.
-Jon
