Electronic hook switch is used to connect a Plantronics headset with a business phone without the need for a lifter. Compatibility Guide: Avaya APV6A - 1608, 1616, 2410, 4630, 5410, 6416D+M, 6424D+M, 9620, 9630, 9640, 9650, 9670 (If phone has Savi adapter, must use APV-62) APV6B - 2420, 4610SW, 4610, 4620SW, 4620, 4621SW, 4622SW, 4625SW, 4630SW, 5420, 5610, 5620 (If phone has Savi adapter, must use APV-65) Cisco APC-4 - 7942G, 7945G, 7962G, 7965G, 7975G (If using a Savi Adapter, must use APC-40) APU-7 - 8961, 9951, 9971 (If using a Savi Adapter, must use APC-70) Nortel APU-7 - 1120E, 1140E, 1150E, 1165E (If using a Savi Adapter, must use APC-70) Cisco/Nortel APU-71 - Savi 700 Series, CS500 Series, CS500 XD Series, MDA200, Savi Office, Voyager Legend CS Siemens APS-1 - Optipoint 410, Optipoint 420, Optipoint 500, Optipoint 600, OpenStage 40, OpenStage 60, OpenStage80 (If using a Savi Adapter, must use APS-10) Toshiba RD-1 - DP 5118-DP, DP 5130-SDL, DP 5X22-SD, DP 5X32-SD, IPT 2008 SDL, IPT 2010-SD, IPT 2020-SD (Uses same adapter when using Savi Adapter)