Passive Box Headset/Handset Switch. Overview:The UI box works as a connector between your handset and headset. At the touch of a button, a passive box will enable you to easily switch back and forth between the handset and headset, or even integrate a PC into the system if you wish.You can choose an active box with additional features that will regulate different volume levels and improve speech intelligibility - automatically.FeaturesThe ultra-compact UI 710 allows you the comfort of quickly switching between using the headset or the telephone handset.Remarkably easy set-upLightweight design with locking switchThe link between your phone"s handset and your Sennheiser telephone headset