The telephone has a set of configuration parameters which are set up by the installer by use of the keyboard.

In order for programming the parameters, do the following:

1 - Hang on the headset and handset.
2 - Press the R button for 2 seconds.
      Red indicator starts to flash.
3 - At the same time press the # key and the parameter number.
     Green indicator the starts to flash.
4 - Enter the parameter value.
     Red indicator starts flashing and You can go to step 3 again 

Parameter numbers are:
2 - headset microphone
3 - headset speakers
5 - handset microphone
6 - handset speaker

Values are:
0 - lowest
8 - highest

Remember that when You increase the volume of the speaker, then you must decrease the gain of the microphone. This in order to maintain stability and avoid howling.