Here's one for you guys out there. I have a Mitel SX2000 Light and am using a Superset 4150. When I plug my Plantronics headset into the headset port on the back of the phone it works fine for a while then the handset starts picking up noise from the headset wen the headset button is off and then mysteriously the handset voice piece stops working. This is the second phone that has done this to me and I know of one other compliant as well. I simply just can't figure this one out.