Ten digits make sense on a telephone. But look at the bottom row of any keypad, and you'll find two extra keys: a star on the left and a pound sign on the right. Today we press them to check voicemail or finish entering a PIN. But why are they there in the first place?
The short answer: Bell Labs added them to send special signals for expected business data-entry uses. The earliest push-button phones for home customers, offered from 1963, left out those two keys. They were added later, and phone companies soon found handy uses for them in calling features built into newer electronic switching systems.
Designing the Push-Button Phone
For decades, Americans dialed with a rotary dial. In the 1950s, researchers at Bell Labs began working on a faster alternative. The modern keypad layout is credited to research by Richard Deininger under John Karlin in Bell Labs' human factors department, a group that studied how people actually use machines.
The result was twelve buttons in four rows of three. The push-button system, known by the trademark Touch-Tone, was introduced to the public on November 18, 1963. Each key sends a pair of tones down the line, which the phone company's equipment recognizes.
Why 1-2-3 Is on Top
You may have noticed that phone keypads put 1, 2, and 3 at the top, while calculators put 7, 8, and 9 there. That wasn't an accident. In the late 1950s, few people had used mechanical calculators, and their layouts weren't even standardized yet.
Bell Labs tested both arrangements and found the telephone layout, with 1-2-3 on top, was slightly faster to use. So that's what went on the phone. The digit keys also kept letters, which once stood for telephone exchange names. Before all-number calling, a phone number in the U.S. might look like KL5-5445.
Why a Star and a Number Sign?
The two extra keys needed symbols. According to one account, the Greek letters alpha and omega were suggested at first. John A. Koten, a communications specialist at Bell Labs in Chicago, claimed credit for choosing the star and the number sign instead. His reasoning was simple: people already knew those symbols from their typewriters, so they'd be easier to explain.
The military even got a version with a fourth column of keys, used for priority calls on a defense phone network in the 1960s.
One Symbol, Many Names
The # symbol has collected a lot of nicknames. Americans call it the pound sign, which likely traces back to an old abbreviation for the Latin libra pondo, meaning "pound weight." Writers shortened it to lb with a line across it, which over time became the crisscross we know.
Bell Labs workers even invented a new word for it by 1968: octothorp. The octo part means eight, but where the thorp part came from is a mystery. One story says it honors Olympic champion Jim Thorpe.
Of course, the symbol found a whole new life online. Inspired by its use in internet chat rooms, Chris Messina proposed using it on Twitter to tag topics, and the hashtag was born.
So the next time you press pound to skip a voicemail greeting, remember you're using a key designed for business data, named after a Roman unit of weight, and later borrowed by social media.
