iBlacklist cydia tweak is the best firewall for iMessages, calls, facetime, SMS and MMS available for the iDevices.
Now it blocks also FaceTime/iMessages and runs on iPod 4 and iPad 2. It ables you to select from who you want to receive calls and hide messages. It also removes the sms popup preview protecting your privacy, has parental control mode by blocking outgoing calls, can be fully scheduled and many other features. Try it , you’ll love it.
Works on any iPhone model running any firmware version !!! PLEASE RESTART YOUR DEVICE AFTER INSTALL. REBOOT IF YOU ARE ON IOS4.