abcGoodefg&reg; Call Center Hands-Free Headset Headphone Desk Telephone Monaural Mic Mircrophone Noice Cancelling Silver 4-pin RJ9(4P4C) Plug, NOT RJ11 plug, directly connect over the head headset headphone, no additional amplifiers or adapters required. Provides all day comfort, clarity and durability for Desk Telephone. Superior quality sound with the flexible adjustable noise cancellation microphone. Comfortable lightweight design, shirt clips included.