Head sets amplifiers boost the signal from the head sets.  All Plantronics H-Series head sets require an amplifier to connect to your telephone. For all Plantronics Call Center Headsets, we recommend the Plantronics M22 or the new Plantronics AP15 VistaPlus. For all GN Netcom Headsets, a GN Netcom 8000 amplifier is required.  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