Yealink YHS34-MONO, Entry-level RJ9 headset, Monaural, Mono earpiece Plug and play, RJ-9 connectivity, Quick disconnect cord, HD voice / wideband speaker performance. Noise cancelling microphone and passive noise cancellation Active protection technology safeguards users from acoustic injury 330° bendable boom arm for easy adjustment without breaking Compatible with Yealink IP phones (T19(P) E2 / T21(P) E2 / T23G / T27G / T29G / T31P / T31G / T33G / T40P / T40G / T41S / T42S / T46S / T48S / T43U / T46U / T48U / T53W / T54W / T57W / T58A / MP56)