Nortel 616 DR4 Key Service Unit (Refurbished)This Norstar KSU is a 6 line, 16 station PBX phone system unit designed for smaller companies that need more than 3 lines but not more than 6 and or need more than 8 stations but not more than 16. These companies or divisions of companies usually expect no future expansion of their phone system beyond the capacity of the 616. More Information This KSU does NOT have disconnect supervision capabilities and includes DR4 Software All norstar phones (M7000