Don't forget to order the proper Plantronics adapter, in my case I needed "Replacement Quick Disconnect Coil Cable For M-12

I tried a cheaper Plantronics headset first the Plantronics M214C Headset with Adjustable Volume, but it proved to be a piece of junk as its volume way too low

I called Plantronics and asked for their recommendation and they recommended either this model or the single earpiece

I specifically looked to see if this headset required an adapter for my 2.5mm compatible Plantronics wireless phone, but I could not find any information on either Plantronics web site or Amazon's.

Let's begin by noting which models are monaural vs. binaural:SupraPlus HW251N - Monaural (1 earmuff), microphone noise reducingSupraPlus HW261N - Binaural (2 earmuff), microphone noise reducingEncorePro HW291N - Monaural (1 earmuff), microphone noise reducingEncorePro HW301N - Binaural (2 earmuff), microphone noise reducingThe W in the model names stands for WIDEBAND AUDIO for which Plantronics claims improvement in sound clarity, etc

Thank you Plantronics for wonderful shipping and quality products.

These work as they are supposed to in my situation, no amplifier needed