Interesting story about the telephone keypad. I think many people would be surprised to learn that so many different alternatives were considered and that different designs were tested for things like keying time, and percent errors. Retromodo: Old American Telephone and Telegraph Report Shows What Keypads Could Have Been
You probably don't think about it much, but there was an intensive selection process that went into the telephone push button keypad. Ironically, the one we use today featured a fairly high error rate.