1) Check Set Up
2) Is there a button labeled “Handsfree” on the phone? This button is the on/off button for the headset and must be depressed before the headset microphone will work.
3) If this does not work then the headset jack may not be turned on. If this is an order that the Customer recently received then this is almost certainly the problem. Only the telephone vendor who installed the phone can turn this jack on.
4) If the Customer has had the headset for a while and his/her mic has suddenly gone out then check the voice tube. It may have become clogged or damaged. Simply have the Customer remove the tube and see if you can hear him/her. If not voice tubes, then do the standard microphone troubleshooting steps.
5) Swap cords around
a). If using a Wireless headset or amplifier swap the black connector cord
b). If using a Headset that connects directly to the phone try another working headset