This feature can be used when trying to reach a phone that is busy or not answered. This feature is also used with voice mail. This is a variation of call forward on don't answer. The speaker phone has volume control activation and deactivation keys and a mute key. These extend the capacity of the multi-line phone by adding 18 additional keys which can be used for line appearances or features.
Stations can have a maximum of three add-on modules.
It is important to note that the terminal adapter does not permit simultaneous operation of the multi-line phone and the peripheral device. For example, the phone cannot be used for a voice call at the same time a modem on the same connection is used to send data. The options include simultaneous ringing, distinctive ringing, programmable ringing per line and continuous ringing on secondary lines while off-hook on another line.