Electronic hook switch ehs cables provide communication between your phone and plantronics headset enabling you to answer and end your calls using your headset call control button ehs cables are designed to work with specific phone models and plantronics products the table below provides the compatibility information for the apc 45 cisco spa512 spa514 spa525g2 cs500 series cs510 cs520 cs530 cs540 savi 700 series w710 w720 w730 w740 w745