I thought that the invention of the number key pad was the greatest invention since Wonder bread. I use it exclusively except when working on the laptop with that damn touch pad. Ever since I learned to type I have always rested my hands on the desk so that reaching the top row of keys is difficult. It is much easier for me to reach the number key pad.

And you are right about the telephone key pad and computer number key pads have different derivations. the computer key pad came from the calculator key pad which came from the old mechanical adding machines. The phone's design derived from the old dial (which we still use on our old style candlestick phone). No common design history. It's like asking why does a plane use a stick, a throttle lever, and rudder pedals while a car uses a wheel and accelerator pedals. (Interestingly enough the original cars used tillers like ships and accelerator levers.)