The M22 Amplifier and H251N Headset make a high-quality Plantronics corded headset system. The M22 Amplifier connects the SupraPlus H251N headsets to just about any modular single- or multi-line phone, and offers easy to use volume, headset/handset, and mute controls. The SupraPlus H251N Headset provides excellent audio quality for traditional voice applications as well as the increasingly popular Voice over IP softphone applications