Either way, it's a wasted question. Years ago, when Ma Bell was the only phone company and they came out with touch-tone phones, they patented the arrangement with 1-2-3 at the top. So if you want to make a calculator that uses that, you'll have to pay a fee.
That's not true. There's no patent for the 1-2-3 keypad (nor was Bell/AT&T the only phone company in the US, but that's not relevant here). Calculators in the form of mechanical adding machines predated the DTMF keypad by decades. When Bell came up with the touch-tone system, they actually spent a lot of money researching whether it should be adding machine layout, or 1-2-3 from the top. As it turned out, even experienced ten-key operators were able to dial phone numbers faster on the 1-2-3 pad because everyone--- even tenkey operators--- approached the task of dialing a phone with their index finger alone, regardless of whether it was pushbuttons or dial, because they were already in the habit of doing so with dial phones. 1-2-3 keypads are faster to use when visually hunting and pecking with one finger. Given that no one was ever going to be doing rapid data entry on a phone, it made more sense to use top-to-bottom order, because the reverse order of tenkey exists only to make rapid multi-digit data entry faster (i.e. zero under the thumb, pinkie for enter, and most common digits under the fingers as per Benford's Law)
I don't know what the hell is wrong with the OP that his brain doesn't have room for two different keypad layouts.