Telephone headset amplifiers boost the signal from the headset. All Plantronics headset require an amplifier to connect to your telephone. For all Plantronics Call Center Headsets, we recommend the new 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