Telephone headset amplifiers boost the signal from the telephone to your headset. All Plantronics headset require an amplifier to connect to your telephone. For all Plantronics H-Series Headsets, we recommend the Plantronics M22. For GN Netcom Headsets, we recommend the GN Netcom 8000 amplifier. They are both compatible with most single and multi-line telephones. Features include mute, one-button selection between head set and handset, separate outgoing/incoming volume controls, easy set up, excellent sound quality and the convenient Quick Disconnect feature. Also See Plantronics Vista M12/M22 Amplifier information page