Today's New York Times has a lengthy story on VoIP only SIP and Skype phones.
One comment I have about many of these phones. The set up is not as easy as it should be. The author points this out, but from my experience, the entire process across the board needs to be made simpler.
Voxilla has a service that can do this, but until every company on the VoIP world subscribes to the same theory as Linskys has arrived at, that of having their own set up system online that really works, the market for these phones will be the early adopter and the true techie.