This article is from the Where to get the latest PGP FAQ, by Michael Paul Johnson firstname.lastname@example.org with numerous contributions by others.
Bill Dorsey, Pat Mullarky, and Paul Rubin have come out with a program
called Nautilus that enables you to engage in secure voice conversations
between people with multimedia PCs and modems capable of at least 7200
bps (but 14.4 kbps is better). See:
The official Nautilus home page is at: http://www.lila.com/nautilus/