Uniden BTHS500 Owner's Manual page 15

Press and hold the Multi-Function button for 2 seconds.
Mobile phone to headset:
f
Press and hold the Multi-Function button for 2 seconds.
MIC Mute
Press and hold volume down for 2 seconds. MIC mute
will then be activated. You can hear the status indication
melody every 5 seconds in MIC mute mode.
You can de-activate MIC mute by pushing and holding
volume down for 2 seconds.
Call waiting (3-way calling)
Before you use 3-way calling function, please make sure
that your mobile phone supports "Handsfree profile". And
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