Plantronics part number 78333-01 is an adapter cable for phones that have a 2.5mm headset jack, such as the Polycom IP 320, 321, 330, 331 models. This adapter allows you to plug in any Plantronics office wireless headset (such as CS50, CS55, CS70, CS70N, CS351N, CS361N or Savi Office) into your phone's dedicated headset jack so you can use your phone's headset button to answer and end calls, or to use with the Polycom hookswitch adapter
for remote call answer/end from the headset. The male modular (RJ9) end of the plug would go into the base tower of the wireless headset.
IMPORTANT: If you want to be able to answer your calls remotely from the headset (without having to be at your desk to press the headset button on your telephone), there is a hookswitch adapter for Polycom IP phones such as IP 320, 321, 330, 331 (see below) that you'll need in addition to the adapter cable above. If you do not have one of these headset port, then do not purchase the above cable adapter nor the hookswitch adapter. Instead you will want to get the Plantronics HL10 automatic handset lifter.