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How do I Set my Samsung SCH-S380C to Silent/Vibrate Mode?
To set your device to Vibrate Mode, press and hold the Space/Vibrate key for one to two seconds. To return to normal mode, press and hold the Space/Vibrate key again.
To set your device to Silent Mode, from standby mode, press the Volume down key, until you see Silence All displayed on the screen. Press to SET the device volume.