Electronic Hook Switch (EHS) cables provide communication between your phone and Plantronics headset, enabling you to answer and end your calls remotely using your headset call control button.
The EHS cable eliminates the need for an HL10 Handset Lifter. (Polycom)
The APP-51 cable works with specific Polycom IP desk phones: SoundPoint IP320/321, IP330/331, IP430, IP550, IP560, IP650, IP670 and VVX1500.
The APP-51 is compatible with the following Plantronics Wireless headsets: SAVI 700 Series, CS500 Series, CS500XD Series, Voyager Legend CS.