Samsung HM1900 Manual page 18

This function is only available on the primary phone.
Answering a call
Press the Talk button to answer a call when a call comes in.
Rejecting a call
Press and hold the Talk button to reject a call when a call comes in.
If you receive calls on both connected phones at the same time you can only
answer or reject the call on the primary phone.
Ending a call
Press the Talk button to end a call.
Options available during a call
You can use the following functions during a call.
Adjusting the volume
Press the Volume up or down button to adjust the volume.
You will hear a beep when the volume level of the headset reaches it's lowest
or highest level.
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