I'm new to this site.
In America It used to be taught to dial "oh" for operator. The area code where I live was called four-of-five.
It used to be that other letters were not used to refer to the numbers except in the local exchage prefix, as in
AL5-7777 which before my time I think was called Alpine-57777. Exchanges had names that I think were mostly used before direct dialing. Now you might here someone say dial 1-800-COLLECT which means 1-800-2655328 using the letters above the numbers to spell a word. I don't know if telephones in countries other than the USA have letters above the numbers or not.
I'm 40 years old.