The article mentions the 1960 Bell System user study of different keypad layouts. I can't speak to the other layouts, but I think in hindsight it's clear why th

The article mentions the 1960 Bell System user study of different keypad layouts. I can't speak to the other layouts, but I think in hindsight it's clear why the "touch tone" layout (with 123 at the top) won over the the "calculator" layout (with 789 at the top). Everyone or nearly everyone in the user study was surely a telephone user. At the time, that meant being accustomed to the rotary dial layout, where the order of the digits is 1234567890. 0 is the last digit, after 9. Both the calculator and touch tone layouts had 0 at the bottom. So the calculator layout has 0 next to 123. The touch tone layout has 0 next to 789 (and following the 9), just like a rotary dial. This must have accounted for some of the preference between these two layouts.