You need to speak to an internal user urgently, even though his line is busy. The "Override" function allows you to interrupt the ongoing call to pass on a message. 

This function is only available when the code has been input and if it has been configured by the service engineer. 

The user is busy. 

Call the function. 

Enter the phone number of the busy user. 

The override is established. The user name or phone number, to whom/which the call has been transferred, is displayed. 

Override is ended when you hang up the handset. 

Note:  During override  all users hear an override tone and everything that is said, all users see the following message on the display "Override:....:".