The function allows you choosing a number that you want in order to
light up during the call to traditional telephones. You can also unlist the
number and it won’t light up.
This is a way of communicating on the half-duplex communication line, includes receiving and transmitting devices (walkie-talkie) by the way of pressing the button for switching to the voice mode or transition to the listening mode. It works as a radio speaker; one can talk by pressing the button and can listen to a voice message by releasing the button.