I am on Peter Shankman's HARO list. This morning there is a UK reporter from Future Intelligence looking for anyone working on Encrypted VoIP in Europe. (Deadline is 9/15). The Editor, Peter Warren, is looking for: "I am looking for any companies that are working in this area and would be very interested in talking to them about why and what they think the opportunities are."
We all know that Skype has some kind of encryption present (AES?), but still has a CALEA back-door.
There is the Zfone project. Zfone (which uses ZRTP) is an open standard. "One of the drawbacks of Zfone technology. In order for a call to be secure, both users have to have the program installed." [VoIPNow]
The other ways to encrypt it are to use VPN, Secure RTP, Transport Layer Security (TLS) and IP Security (IPSec).
In addition, here in Tampa Bay, we have a the developer of DOD (Defence Dept.) level security for VoIP Calls. It is called myKryptofon by ID Rank Security, who promises NSA level security - and is providing that for the DOD now.