Amplifier only.  Easy to install and use. Compatible with almost all phone systems and a variety of Plantronics headset styles. Easy adjustability. Separate controls permit independent adjustment of transmit and receive volumes. Easy one-button select for headset or handset function. Easy to hear and be heard. Soundgard Plus and Call Clarity technologies set a new standard for sound quality. Easy on the ears, too. Automatic gain control system keeps incoming sounds at comfortable hearing levels..  Good used working condition.