a new secure VoIP phone software product which lets you make secure encrypted phone calls over the Internet. It lets you whisper in someone's ear from a thousand miles away. Zfone enables you to have a private conversation any time you want with anyone, anywhere ? without buying a plane ticket. The ZRTP protocol used by Zfone will soon be integrated into many standalone secure VoIP clients, but today we have a software product that lets you turn your existing VoIP client into a secure phone. The current Zfone software runs in the Internet protocol stack on any Windows XP, Vista, Mac OS X, or Linux PC, and intercepts and filters all the VoIP packets as they go in and out of the machine, and secures the call on the fly. 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 on the fly. 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 wire", sitting between the VoIP client and the Internet. Think of it as a software bump-on-the-wire, or a bump in the protocol stack.