Please refer to the Plantronics Compatibility Guide for the correct cable

Electronic HookSwitch (EHS) communicates electronically with the phone, eliminating the need for a HL10 lifter

Cisco IP : 8961, 9951, 9971
Avaya/Nortel: 1100 Series, 1120E, 1140E, 1150E, 1165E
EHS Cable for CS500/Savi 700 Series