My friend Aanu Adepoju from Nigeria writes:
 
This your last mail got me thinking seriously about something that has been around and has been a large cash-cow for a while, and I have not paid any attention to whatsoever. Call termination.

How does it work, in your words. I have this really vague idea abt the whole thing. That calls to public phone systems across the world are passed over IP/internet, and routed to the other end's phone exchange, in our case here, routed to NITEL, PTOs and the new GSM guys.