At the Black Hat Briefings event in Vegas this Thursday, PGP godfather Phil Zimmerman is expected to present a prototype system for encrypting VOIP phone calls:
Like PGP and PGPfone, which he created as human rights tools for people around the world to communicate without fear of government eavesdropping, Zimmermann hopes his new program will restore some of the civil liberties that have been lost in recent years and help businesses shield themselves against corporate espionage.
Here's the Wired News story, Here's the CNET piece.