You can block calls to your handset on a temporary basis, while still being able to make calls yourself. Internal callers hear the busy tone, while external callers reach another telephone defined by the service engineer (intercept position). Authorised internal callers automatically override the do not disturb after five seconds. 

Activating do not disturb

Press the Talk key. 

Call the system menu. 

Select and confirm the menu item. 

Press the On-hook key to end the process. 

Deactivating do not disturb

Press the Talk key. 

Call the system menu. 

Select and confirm the menu item. 

Press the On-hook key to end the process.