Zfone is a VoIP phone software to help you keep in touch with your friends. Zfone is a new secure VoIP phone software product which lets you make encrypted phone calls over the Internet. Its principal designer is Phil Zimmermann, the creator of PGP, the most widely used email encryption software in the world. Zfone uses a new protocol called ZRTP, which has a better architecture than the other approaches to secure VoIP.

The ZRTP protocol has some nice cryptographic features lacking in many other approaches to VoIP encryption. Although it uses a public key algorithm, it avoids the complexity of a public key infrastructure (PKI).

You can use a variety of different software VoIP clients to make a VoIP call. The Zfone software detects when the call starts, and initiates a cryptographic key agreement between the two parties, and then proceeds to encrypt and decrypt the voice packets. It has its own little separate GUI, telling the user if the call is secure. It's as if Zfone were a "bump on the cord", sitting between the VoIP client and the Internet. Think of it as a bump in the protocol stack.

The license of this software is Freeware, you can free download and free use this internet phone software.