Nice post...Although I don't think I would classify this as a tutorial. It seems to me more like a position paper. (like you are trying to prove a point). All I am saying is that perhaps it would be better suited for a different forum.

The key here and the main problem with the concept of VoIP over the Internet is the QOS factor. There is not currently, nor will there be any time soon (if ever) a way to give certain types of traffic priority over others through the Internet. After all, who's to make the decision that your VoIP traffic should have a higher priority than my FTP traffic (just an example)