The new Confide iOS app for iPhone, iPad and iPod Touch is a free message-deleting IM app.
With "Confide: Your off-the-record messenger" you can send text messages to any e-mail address, either by choosing someone from your contact list or manually entering the address.
But to read your message, your recipient must also sign up for a Confide account and download the app. Viewing a message for the first time prompts them to do so.
After the message is closed, it disappears for both the sender and the receiver. The messages themselves are private and encrypted.