Re: [Dadsy] Privacy
It's a good piece of software written by the security genius Moxymarlinspike.
Edward Snowden recommends it (I don't care about anyone's opinions about his actions) but you can't get a better balance of security-knowledge, motivation and paranoia to make an opinion on this stuff.
Signal works on iOS and Android and does a great job with both audio and text (the Android versions used to be called TextSecure and RedPhone).
It you want to have secure communications, this is about the best you'll find on a smartphone; but depending on your location, you can be compelled to reveal your password(s).