Universal Business Phone Handset/Headset Amplifier - Model UA-50

Amplify your business phone or headset for loud, clear office calls.

The only universal amplifier that works with both handset and headset. Increases incoming voice up to 45+dB without static or distortion. Compatible with virtually all modular corded phones and external headsets. Digital Sound Processing and Tone Enhancement for speech clarity. Automatic Gain Control optimizes volume level.

Source:- https://www.sereneinnovations.com/universal-business-phone-handset-headset-amplifier.html