Looking at old rotary phones they only had 0-9, but modern (touch tone?) phones also have * and #.
Why / when were they added? What was the first use case?
Were there arguments over adding these?
They had 8 tones in a grid.
4 x 4
Each button was a combination of a row tone and a column tone.
So from 8 tone generators you got 16 unique tones.
Civilian phones were 4 x 3 for 12 unique tones.
The bottom row only had the number 0, but the phones were capable of 2 extra unused tones. Early phones had no buttons in the * and # spots.
As time went on, Bell found a use for the 2 extra tones so then they added the * and # buttons.
In 1961 inventors at Bell Labs had to pick something to go there so they just chose two symbols found on a typewriter. They went with * and #. From what I read they chose them based on business usage at the time.
Kind of as a joke, Bell scientists eventually officially named them: