Poly/Plantronics APP-51 EHS For Polycom Desk Phones #38439-11
Compatible with CS500 & Savi series, MDA200 and Voyager Legend CS wireless headsets. Electronic Hook Switch Cable for remote desk phone call control (answer/end). This cable eliminates the need for a HL10 Handset Lifter. Works with Polycom desk phones and may work with additional manufacturers.
For more information download the EHS Guide here
For complete compatibility info click here