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The standard layout of the keys on the touch-tone telephone was the result of research of the human-engineering department at Bell Laboratories in the 1950s under the leadership of South African-born psychologist [[John Elias Karlin]] (1918–2013), who was previously a leading proponent in the introduction of all-number-dialing in the Bell System. This research resulted in the design of the [[Dual-tone multi-frequency signaling|DTMF keypad]] that arranged the push-buttons into 12 positions in a 3-by-4 position rectangular array, and placed the 1, 2, and 3 keys in the top row for most accurate dialing.<ref>{{cite news| url=https://www.nytimes.com/2013/02/09/business/john-e-karlin-who-led-the-way-to-all-digit-dialing-dies-at-94.html | work=The New York Times | first=Margalit | last=Fox | title=John E. Karlin, Who Led the Way to All-Digit Dialing, Dies at 94 | date=February 8, 2013}}</ref> The remaining digits occupied the lower rows in sequence from left to right; the 0, however, was placed into the center of the fourth row, while omitting the lower left and lower right positions.{{citation needed|date=November 2020}}
The DTMF keyboard layout broke with the tradition established in cash registers (and later adopted in calculators and computers) of having the lower numbers at the bottom.<ref name=straightdope>{{Cite web|url=https://www.straightdope.com/21343156/why-do-telephone-keypads-count-from-the-top-down-while-calculators-count-from-the-bottom-up|title=Why do telephone keypads count from the top down, while calculators count from the bottom up?|first=Straight Dope|last=Staff|date=July 16, 2002|website=The Straight Dope}}</ref> This was due to research conducted by Bell Labs using test subjects unfamiliar with keypads. Comparing various layouts including two-row, two-column, and circular configurations, the study concluded that while there was little difference in speed or accuracy between any of the layouts, the now familiar arrangement with 1 at the top was the most favourably rated.<ref name=belltechnical>R. L. Deninger, [http://
The engineers had envisioned telephones being used to access computers, and surveyed business customers for possible uses. This led to the addition of the [[number sign]] (#, ''pound'' or ''diamond'' in this context, ''hash'', ''square'' or ''gate'' in the UK, and ''[[octothorpe]]'' by the original engineers) and [[asterisk]] or ''star'' (*) keys in 1969.{{citation needed|date=November 2017}} Later, the hash and asterisk keys were used in [[vertical service code]]s, such as ''*67'' to suppress [[caller ID]] in the Bell System.{{citation needed|date=November 2020}}
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