What is "hush-a-phone"

The Hush-A-Phone was a device designed to attach to the receiver of a telephone to reduce noise pollution and increase privacy. Sold by the Hush-A-Phone company, the device was frequently described in its commercial advertisements as "a voice silencer designed for confidential conversation, clear transmission and office quiet. Not a permanent attachment. Slips right on and off the mouthpiece of any phone".

The device was the topic of a landmark court case, Hush-A-Phone v. United States. The Hush-A-Phone was regularly referred to in telecommunications policy analysis in the 1980s, attracting renewed interest in the 2000s as a symbol of a small company fighting against a monopoly, especially in the context of net neutrality. Indeed, because Hush-A-Phone eventually won its case against the phone company, the final legal proceedings involving the Hush-A-Phone turned out to be relevant to the eventual breakup of the Bell system.

Advertisements for the Hush-A-Phone not only argued for its importance as an aid to privacy, but also noted the device improved clarity of sound, which AT&T would directly argue against.