The Do Not Disturb or (DND) function of our VoIP phone systems prevents calls from ringing an extension for which DND is activated. Some of the Do Not Disturb (DND) attributes include directing the call to a pre-assigned extension (like a secretary or assistant), busy signal, DND signal, or recorded message generated by the telephone switch. Some switches allow the call to go through to the extension but restrict the response to a visual indication.