Yesterday I tried TextSecure. The nice thing about it: It replaces your SMS app if you want, so you have one app to do all your text messaging. If the recipient also uses TextSecure the message will be end-to-end encrypted automatically. If you don't have a data connection the message will be send via SMS/MMS, again encrypted if the recipient supports it. Of course it also supports group chats and you can send pictures, video and audio messages. And it is all Free Software!

Only drawback for mass adoption: No iPhone and Desktop client at the moment... But they are already working on it and it should be available soon.

Open WhisperSystems >> Blog >> The New TextSecure: Privacy Beyond SMS

Blog >> The New TextSecure: Privacy Beyond SMS. Today's release of TextSecure is the final step in the transition from a private SMS app to a private asynchronous IM app that does not depend on SMS/MMS. Using the lessons we've learned from the SMS environment over the past four years, ...