Plantronics headset connected to Mitel 4025 - won't work!!!!

You need to have a headset button on the set, and you need a release button if you want to transfer calls to others.
Press the Blue SuperKey and press all the buttons (one at a time) to find a spare button or find one that you do not use or need. Press the * button to change the button (scroll thru the options to find headset).
Once you made the button in to a headset button, press button to turn on or off the headset. Once the button is lit up, this means that the headset is active, now try pressing the call with the receiver off hook.
This should do the trick... if not write back and I will attempt to help you more.
Good Luck!

You need a headset key on the phone..