I just saw this at MIT's Technology Review and thought to share.

Phillip Zimmerman has just released, on May 21st, but Technology Review posted the article today, for secure telephone over the Internet - Zfone, which:

I've just released a new public beta for Zfone, a new product that takes a new approach to make a secure telephone for the Internet. Zfone lets you whisper in someone's ear, even if their ear is a thousand miles away.

Zfone uses a new protocol called ZRTP, which is better than the other approaches to secure VoIP, because it achieves security without reliance on a PKI, key certification, trust models, certificate authorities, or key management complexity that bedevils the email encryption world. It also does not rely on SIP signaling for the key management, and in fact does not rely on any servers at all. It performs its key agreements and key management in a purely peer-to-peer manner over the RTP packet stream. It interoperates with any standard SIP phone, but naturally only encrypts the call if you are calling another ZRTP client. This new protocol has been submitted to the IETF as a proposal for a public standard, to enable interoperability of SIP endpoints from different vendors.
MIT Technology Review Article: http://www.technologyreview.com/read...&id=16948&pg=1

Zimmerman's Web Page detailing Zfone: http://www.philzimmermann.com/EN/zfone/index.html

And while we know VoIP is not new Zimmerman has a few changes - from the MIT article :
VoIP encryption isn't new -- Skype, the most popular VoIP service uses encryption -- but Zimmermann's software issues encryption keys that bypass the servers routing Internet calls and sets up the encryption directly on the voice channel.