The electronic hook switch (EHS) cable for Polycom telephones is used with a Jabra wireless headset and connected to the telephone to enable remote call answering.
This means that you can be away from your desk, wearing your wireless headset and hear the telephone ring in your headset. At the touch of a button you can answer that call and when finished hang up, all without returning to your desk.
To see how this is set up with Polycom telephones view the PDF on the below.
Not all Polycom telephones are configured to use EHS cables. This PDF also identifies which telephones you can use this EHS adapter with.