This is the Norstar 616 Control Unit for Nortel business phone systems. This phone cabinet has the capability of 6 lines and 16 extensions, but lacks "Disconnect Supervision" (or DS) which is used by Voicemail Units to hang up calls. Because this cabinet is non-DS it will not work with Voicemail units (for voicemail compatability use the NS616DSKSU instead). Software is required to use a 616 cabinet and is not included. The following Norstar phones will operate on this control unit (Meridian M7100, Nortel Meridian M7208, Norstar Meridian M7310, Norstar Meridian M7324, Nortel T7100, Norstar T7208 Black, Nortel T7316E, NST7406CHN).