Universal Home Phone Amplifier - Model UA-45

Instantly turn your home phone into an amplified phone.

Converts virtually any corded landline telephone into an amplified phone. Enjoy louder, clearer conversations with volume amplified up to 45+dB. The tone control switch enhances low to high frequency for added clarity. The unit connects easily between the handset and base.

Source:- https://www.sereneinnovations.com/universal-home-phone-amplifier.html