GreatCall Jitterbug Manual page 65

The selected volume level will appear on the Inside Display.
The ringer can be silenced by pressing the volume button down until
"Vibrate" appears on the Inside Display. Your Jitterbug will now only
vibrate to alert you of incoming calls. This can come in handy at a movie,
a library or any other location where a ringer may be a distraction.
Placing And Receiving Calls 55