PrivateSMS is an interesting Cydia tweak allows us to hide the list of SMS and avoid posting new messages. While in the Messaging application, pressing Edit button will appear a new lock, which if left blank down the list of messages sent and prevent new ones from there.
To reverse this effect, you press the Edit button and then the Unlock button. No icon or options to configure, simple and easy for users who want to avoid prying eyes on your message list.
The tweak is in the BigBoss repo, Cydia installed by default, so you just have to go to Search, type PrivateSMS and install, is free. After the installation, restart Springboard and have the option available.