From Mobi Shhh:
Shhh! encrypts your plain text messages and transmits them securely, bypassing the SMSC storage system completely, leaving no trace. All standard SMS messages are stored in a readable form on your cell phone providers short message service center (SMSC), computers. It varies from country to country and provider to provider as to how long the content and detail is retained. Even during transmission over the GSM network security is not guaranteed as the GSM encryption ciphers A5/1, A5/2 and A5/3 have also been proved to be vulnerable. An even easier interception approach is simulate a cell phone base station also known as an IMSI catcher which can force your phone to use A5/0 mode (no encryption), the details of how to do this are freely available and can be achieved at little cost. While there are legitimate reasons for authorities to access stored and transmitted information, there are also legitimate reasons for individuals to have the option of communicating privately without the possibility of intrusion on that basic human right. Shhh! has been created to facilitate that option. Besides the potential threat of authorized national or international interception there is also the far greater threat posed by corporate spies and cyber criminals to consider. Regardless of whether your on a GSM or CDMA network the service we provide is essential to secure the exchanging of commercially sensitive information, confidential legal or financial transactions and general personal private communication.