Why do phones and calculators have different number layouts?

Answer 1

Data-entry professionals, and others who used calculators fairly regularly, were quite adept at navigating keypads (7, 8 and 9 across the top row). They could hit the numbers extremely quickly, which was great for data entry, but not so great for dialing a touch-tone phone. The tone-recognition technology could not operate effectively at the speeds at which these specialists could dial the numbers. The telephone designers figured that if they reversed the layout, the dialing speeds would decrease and the tone-recognition would be able to do its job more reliably. This theory has little proof to substantiate it, but it does make sense... vipulsahu@iitr

Answer 2

This was done to slow people down. Originally, the phone system could not handle the high speed that Accountants were dialing, so the keypad layout was reversed.