Der Werdegang der mobilen Kommunikation
Unterwegs telefonieren – Die Geschichte des Mobiltelefons
Vom Zug ins Auto, in die Hand: Die Entwicklung des Mobiltelefons bis zum Smartphone
https://www.digitales-museum-fuer-kommunikation.de/expotizer-unterwegs-telefonieren/

Der Werdegang der mobilen Kommunikation
Unterwegs telefonieren – Die Geschichte des Mobiltelefons
Vom Zug ins Auto, in die Hand: Die Entwicklung des Mobiltelefons bis zum Smartphone
https://www.digitales-museum-fuer-kommunikation.de/expotizer-unterwegs-telefonieren/

@t_bias @anon_opin This is a neat writeup on the user studies conducted regarding phone keypad layouts (at least in the US):

https://www.todayifoundout.com/index.php/2015/10/keypad-numbering-different-phones/

As for calculators, while it was highly unlikely to be been a conscious justification, Benford's Law indicates that digits 1, 2, and 3 will be the first digit many classes of number representing quantities, 60% of the time (it's even been used to detect fraudulent accounting). It's possible that long before this was known, it was just experienced, and that influenced cash register key layout which carried over to calcs. That's just a guess, but I'm very thankful that calc keypads have the convention they do.

https://en.wikipedia.org/wiki/Benford%27s_law

@t_bias @anon_opin This is a neat writeup on the user studies conducted regarding phone keypad layouts (at least in the US):

https://www.todayifoundout.com/index.php/2015/10/keypad-numbering-different-phones/

As for calculators, while it was highly unlikely to be been a conscious justification, Benford's Law indicates that digits 1, 2, and 3 will be the first digit many classes of number representing quantities, 60% of the time (it's even been used to detect fraudulent accounting). It's possible that long before this was known, it was just experienced, and that influenced cash register key layout which carried over to calcs. That's just a guess, but I'm very thankful that calc keypads have the convention they do.

https://en.wikipedia.org/wiki/Benford%27s_law