SIP is Session Initiation Protocol. It is a rather common (and in my opinion one of the better) protocol used in VoIP. Take this SIP address for example:
If you were on my local network and setup on my VoIP server, that's how you would reach me. Of course, if I had it setup to POTS, you could call me from anywhere, but this is offtopic
Take this IAX example (another VoIP protocol, which is Inter-Asterisk eXchange):
What you suggested above is more IAX than SIP I suppose, but kind of a combination of both. I personally prefer SIP over IAX since IAX (pronounced eeks), is created for Asterisk and it isn't widely available on other VoIP platforms, along with other problems, but SIP has its own problems with NAT traversal is such, but eh, you get the idea. Not to mention offtopic again.
I think this could be really interesting. If I had time, I'd offer to help, but I really don't.