SecretSMS – Send Encrypted Text Messages On Your iPhoneMonsta'd on February 24th, 2011
SecretSMS is an iPhone/iOS tweak that allows you to encrypt your SMS text messages as you send them. The recipient of the message won't need to have any extra software or apps installed on their mobile device, they will just need to know the password to see the content of the message. Any kind of mobile device can decrypt the message.
We really can't think of a time where we would need to send a "secret" text message, but for you security-conscientious iPhoners out there (or spies!), SecretSMS may be something you want to take a look at.
It's worth pointing out that a Chinese company called TrustMobi is the developer and service provider behind this app. Keep in mind that the SMS messages you are encrypting will be sent to their servers [for encryption], as you can see in the screenshots above.
SecretSMS is available for free in Cydia, via ModMyi.