Why does the iPhone calling screen have letters under the numbers?

The letters are there to just help you memorize the phone number. For example, 567–789-FAST (not real number) should be dialed as 567-789-3278. It is a standard feature of every phone to have letters under the digits in the phone app or non-smartphone.

1. Why does the iPhone dial pad have alphabets?
2. Why do phone keypads have letters under each number?
3. How do I change my keypad from numbers to letters?

Why does the iPhone dial pad have alphabets?

What is the use of phone keyboard dialing alphabet. I may be misunderstanding your question but if you mean the letters below the numbers on the phone keypad (e.g. the "ABC" below the 2), one use of them is for companies to advertise with easier to remember numbers.

Why do phone keypads have letters under each number?

The exchange names did more than provide a phone number. They identified the area of the city where you lived. And, if you have ever wondered why telephones have letter designations it is a leftover from the days of alphanumeric phone numbers, when people needed to know which letters were covered by which numbers.

How do I change my keypad from numbers to letters?

When you press the 'U, I, O, J, K, L…' letter keys on the right side of keyboard, occasionally numbers can come up instead. This situation usually occurs when Num Lock has been enabled. To solve this problem, you should turn Num Lock off. To disable Num Lock, press the FN key and F11.