Here in the UK, for example, 21CN's changed the network so that all phone calls go over VoIP, but not over the Internet - they go over the same cables, protocol

Here in the UK, for example, 21CN's changed the network so that all phone calls go over VoIP, but not over the Internet - they go over the same cables, protocols, etc, but it's a private, internal service (imagine your ISP runs a 10.* network internally, and your phone line is connected to that).