It's actually a MIK key, not MIC. You put a MIK and a MCK key on any telephone and see if you can light the light. Once you have defined the MIK key on a phone you press it while on hook, dial the ext# you want to light the light on and then press the key again. If you look at the phone the MW indicator should be on. Then press the MCK key, dial the ext # and press the MCK key again to turn it off.