To put a call on hold, press the Hold softkey. The hold icon appears and the LED indicators pulse green. 

If there is only one call on hold, press the Resume softkey. 

You can swap between holding and active calls by using the Swap softkey.  The holding call becomes active, and the active call is placed on hold. 

The conference station can be muted in two ways:  you can either press the Mute button on the Sound Base or on the Display Control Unit. The LED indicators on both pieces will illuminate red when the sound is muted.