On rotary phones, the 7, 8, 9, 0 took forever!
With a little practice, you could tell what number someone was calling just by listening to the phone being dialed.
That’s why area codes with 1 in the middle were assigned to areas which got the highest call volume. Areas with the highest call volume got lower numbers for the other two digits. Chicago got 312 and NY got 212, LA got 213.
DC, on the the other hand, got 202. Virginia got 703 (for the entire state).
It was a lot quicker for the switching equipment to set up a call to a 212 area code than to a 703 area code.
It doesn’t matter these days, but it did when area codes were first assigned.