We would like to build an application for your cell phone that allows you to message someone over secure / encrypted methods. It will include text messages (meaning, messages in the form of text, not text messages through you phone service) and voice / audio calls (meaning, the voice signals will travel through the app, not the cell phone signals).
This is a prototype, so we can smash together any open source code available (so long as the license allows for us to use it). For example:
http://speak-freely.sourceforge.net/ (old stuff never really got finished)
http://www.speex.org (we can use to compress the audio data)
https://jitsi.org/ (we would need to strip this down quite a bit)
In addition, we will need to encrypt the data and use other techniques, including vpn tunnels, hops, etc.