I don't think this is so much an explanation of VoIP as it is VoIP *networks*. The "asterisk" software that's described can be used to replace an office phone system. Except that the "office" with this network doesn't have to be confined to one building. The office can be virtual with each cubicle located anywhere in the world.
The author makes the point that as long as he is only communicating with people tied into his virtual phone network, the communications never enter the standard telephone grid, and therefore doesn't pass the fed's wire tappers. In fact I don't think he can call into the phone grid from his network phone unless I missed that.
What's interesting to me is the likelihood that two of these virtual networks (i.e. two "businesses" each with their own internet based phone servers or phone "centers"), might be free to interact with one another without going through the telephone grid. If so, then the stage is set for the complete demise of the telephone grid itself, as all phone communications would/could just be made from one internet phone server to another internet phone server just like email today never enters the phone grid. All transpires solely over the internet.
What's interesting to me is the likelihood that two of these virtual networks (i.e. two "businesses" each with their own internet based phone servers or phone "centers", might be free to interact with one another without going through the telephone grid.
Intriguing, but I don't see landlines going away anytime soon.
I would like to try out what he's doing with his own phone server, or network.