A very detailed analysis of the recent VoiceWing announcement is offered up by Faultline, a research company.
While it appears to deposition cable companies such as Cablevision's offering, one that works and uses a managed network built out by Cablevision, and which likely has very high level peering partnerships with the other MSOs and tier one carriers, the article misses one key point. No managed network. And that's where QoS is really a factor. Heck, even Skype uses managed networks for their termination and it would seem their on net calls, and the latter are free.