To enable the Do Not Disturb feature (DND),

• Select the Phone Option Setting and check the “Do Not Disturb” check box. Then press the Apply button.
• Enable/disabe it from the contextual menu
• Use the key shortcut ALT+D

All the incoming calls will be rejected.
You will have visualization of the status on the display with the “DND icon”

If configured in Asterisk the extension button will change his status.