This is the Compact ICS control unit for Nortel phone systems. It 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 maibox can be put on your system. No more monthly fees to the telephone company for that voicemail on your line. This system is also voicemail compatible. Model NT7B58.