AT&T 92021 Behind-the-Head Headset - Metallic Charcoal Headbands fits around the back of your head for greater comfort and mobility Works with many cordless or cellular telephones with an audio jack accommodating a 2 1/2 mm plug Volume Control with Mute increases the incoming volume by about 30 per cent Noise cancelling microphone captures natural voice quality, helps eliminate echoes and filters room Adjustable microphone arm and ear piece allow use on either ear