The Compact ICS control unit has a maximum capability of 8 lines and 24 extensions. The control unit has a built in automated attendant which is a very desirable feature either for business hours or after business hours. This feature allows customers to direct their own calls to their desired extension. There is also an analog port built-in to the control unit which will allow for an answering machine to be hooked up and a general mailbox can be put on your system. The Compact ICS system is also voicemail compatible.