CameraMuteApp mutes the camera shutter sound on GSM devices, so on all NON xx30 devices.
Launch the app, then press Menu -> Add MenuItem then you go to your camera app. Now when you want to mute the sound of the shutter you simply click Menu -> Mute! and after you have taken the photos you click Menu -> Unmute! to turn on the sound again.
After each reboot you have to add the MenuItem to the Menu again