Replacement T100 Headset Headphone Ear+Adjustable Volume+Mute Control Phone for Nortel Networks Nt Nothern Telecom Meridian PBX Norstar Nec Electra Mitel Polycom Toshiba Avaya Lucent Voip IP Telephone Direct Connect Over The Head Headset, No Additional Applifiers / Adapters Required Built-In volume adjustable and mute button control. Shirt clip included. Soft Leathered Ear Cushions For All Day Comfort Superior Quality Sound with the Flexible Adjustable Microphone Headband Style with Single Earpiece for Great Sound Quality in One Ear. Please see compatible phone model in description.