Another app for secret texting is Blink. It's claim to fame is self-destructing messages that disappear after a certain time period. This leaves no permanent record of the text, photos and videos you send. Its also free for Android and iPhones. It adds hacker-proof encryption to everything you send through the app.
One more - WICKR. This one is really simple to set up and use and claims military strength encryption. You can send those disappearing messages and control just who can read your messages and for how long. The motto for this app is "Leave no trace." Its for the iPhone and Android and is free.