external buttons 
If the external display times out while you are using the external buttons, press the smart/speakerphone key to turn it back on.
Tip: Lock the external buttons when not using them so you don’t accidentally activate them when the flip is closed. To lock the buttons, press and hold the smart/ speakerphone key. Press and hold the smart/ speakerphone key again to unlock them.
mute button
During a call, press the mute button 
to mute your voice. Press the mute button again to unmute your voice.
When the phone is idle, press and hold the mute button 
to change the Master Volume setting to Vibrate Only. Press and hold the mute button again to switch back to the previous ringer setting.
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