Plantronics APP-51 EHS Cable For Polycom
Electronic Hook Switch- communicates electronically with the phone
Eliminates the need for a HL10 lifter
Enables One Touch Remote Call/Answer with Plantronics Headsets **
Plantronics APP-51 EHS Cable For Polycom
Electronic Hook Switch Cable for remote desk phone call control (answer/end). This cable eliminates the need for a HL10 Handset Lifter.
This cable works with Polycom desk phones.
Replacement Note: The APP-51 EHS cable replaces the APP-50 cable and features compatibility with the Plantronics On-line Indicator accessory.
**one touch headset answer may not work on all Horizon VVX firmware 

Works With The Following Polycom Telephones:
SoundPoint IP 320/321
SoundPoint IP 330/331
SoundPoint IP 430
SoundPoint IP 450
SoundPoint IP 550
SoundPoint IP 560
SoundPoint IP 650
SoundPoint IP 670
VVX 1500

Works with the Following Plantronics Series Headsets:
Savi700
CS500
MDA200
Savi office
Note: 
After connecting the adaptor on the phone go to Menu then
  1. Settings
  2. Basic
  3. Preferences
  4. Headset
  5. Hookswitch Mode
  6. Select Plantronics EHS
  7. the phone will restart with the new settings