Here is a good article about a software product that may help with surveillance concerns while trying to have a legal private phone conversation.
As Phil says, "Zfone is the software that implements my new encryption protocol, called ZRTP, in a certain way. Zfone is not a VoIP client; it watches for the packets of Internet data going in and out of the machine and looks for ones that are VoIP related. Upon detection of a VoIP call, it intercedes to encrypt the call by setting up a key agreement in the media stream and encrypts the packets of voice data. As time goes on, you'll start to see ZRTP inside VoIP clients. I have a software development kit that people can stick in their VoIP clients."
link to www.technologyreview.com
Just as interesting as the product and its use is the developer of this software Phil Zimmerman
Check out this link that tells a little about some of his efforts in which he is:
Keeping Up The Good Fight
Check the FAQ page from his website that broaches the fatal
"What about if a backdoor was written into the program?"