SS7 - Signalling System 7 is the way that telephone switches talk to one another. http://www.pt.com/tutorials/ss7/ explains how it works (at a high level).

Margin Management - how could I not plug the company I'm working for? http://www.blackinksystems.com/ makes software that helps carriers make more money.

VOIP - voice over IP is an interesting technology. I spent a few weeks playing with some open-source software written by a company called Vovida, and it's pretty darn cool. http://www.vovida.org/

-- TobyCabot - 13 May 2002