Plantronics M12 Vista Amplifer and H91 Encore Voice Tube Headset M12 connects Plantronics headsets to most single or multi-line telephone Easy to use, featuring ergonomically designed volume, headset/handset, and mute controls This amp includes both the coiled Quick Disconnect cord and the standard short pigtail cord. It also offers all-day comfort and superior sound quality. Lightweight over-the-head single earpiece design for comfortable extended-wear use. Features Voice Tube microphone technology and Single earpiece headband style