NetworkComms.Net does not implement a specific VoiP protocol in and of itself, it does however allow you to send custom objects via either TCP or UDP. As such you could therefore write your own VoiP protocol should you wish, without the hassle of working with low level objects like Sockets.
I’m sure however many would say you shouldn’t do this as there already exists a set of open standards. Ultimately it depends on your application and how much compatibility you want with other products and whether you need to implement features that are incompatible with existing protocols.
Hopefully this helps