EPOS | Sennheiser UI 710 Passive Box

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. These boxes are absolutely user-friendly because they are easy to set up than traditional boxes.

NB Connector cable from headset to passive box is required. This is dependent on the model of phone that you have.