Why is Telephone Keypad and Calculator Keypad Different?

Have you ever noticed that telephone keypad and calculator keypad are different? ;)

There are many theories explaining this difference, we will jot down some of the points.

The First Theory on Telephone Keypad

The first theory deals with the telephone's circuitry and tone-recognition hardware. When the touch-tone telephone were being designed in the years of 1950s, the calculator designers had already established a layout that had 7, 8 and 9 across the top row of the keypad, Data entry people and others who frequently used calculators were quite adapt to this keypad and its navigation style.
This was a problem because these people could hit up their numbers very quickly as they were quite comfortable with the navigation style of calculator keypads but the telephone keypad had a problem in it, The telephone keypads did not recognize the fast typed numbers, The tone dialing technology present in these keypads were not effective in picking up quick number dials on keypads hence the pace had to be slowed down to increase the effectiveness of them.

That is why the layout of telephone keypad had to changed (infact reversed) inorder to make them effective at their work with telephones.