Plantronics APP-51 Electronic Hook Switch (EHS) cable for Polycom Phones - communicates electronically with the phone, eliminating the need for the HL10 lifter. This cable is compatible with Plantronics Savi WO100,WO200, WO300,WO350, W740, W730, W720 W710. It's also compatible with the new CS540, CS530, CS520 and CS510 wireless headsets. Do not order this part if you don't have any of these headset models. Compatible with the following Polycom models: SoundPoint IP 320/321*,SoundPoint IP 330/331*, SoundPoint IP 335, 430, 450, 550, 560, 650, 670 VVX500 & VVX1500
Note: If you have a Plantronics "CS" Wireless Headset (CS55, CS351, CS70 etc.) you will need the Plantronics APP-5.
* The 320 and 330 require a 2.5mm to FJ-9 adapter(Polycom Cube)