TXTCrypt is a free app for Android, iPhone, Palm and desktop computer to encrypt any text message, from SMS up to notes, an online version exists to encrypt/decrypt messages if you do not want to download the app.TXTCrypt uses RC4 for encryption, a malleable and quick stream cipher designed in RSA laboratories, these days it is not considered secure enough to withstand a state sponsored attack on your communications but it should stop the average hacker.
TXTCrypt uses symmetric encryption, where you password protect your text message and it can be decrypted by anyone who knows it, a system will have to be designed to pass on the password, which should be as long as possible to employ the full 64bit cipher strength.
TXTCrypt mobile phone text encryption
While more secure encryption apps exist, TXTCrypt appeal lies on its simplicity and multiple platform support, being available as a Java download means that this program will run in obscure operating systems like Solaris and FreeBSD, adding to Windows, Mac and Linux.
Being available for desktop as well as mobile phones it is also a strong point, as long as your security needs are low this is a good app, otherwise search for an encryption app using the AES cipher.
TXTcrypt now on Windows Phone http://www.windowsphone.com/s?appId=14f88d59-de37-4d62-86b4-2d90669b396b