Zfone is a new secure VoIP phone software product which lets you make secure encrypted phone calls over the Internet. Zfone is not itself a VoIP client, but lets you make secure calls with your existing VoIP client, by filtering, encrypting and decrypting all your VoIP media packets as they pass in and out of your computer. You can use a variety of different software VoIP clients to make a VoIP call. 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.