You can activate the do not disturb function if you do not want the receive any calls. When do not disturb is activated, internal callers hear a busy signal and external callers are rerouted to a telephone assigned for this purpose (System Support). 

Select and confirm. 

Enter the code for "on" or "off". 

When you lift the handset, a special dial tone (continuous buzzing tone) reminds you that do not disturb is active.  Authorized internal callers can automatically override the do not disturb function after five seconds.