Telephone exchanges in the USA used to feature two initial letters, and if you have an old-fashioned dial or pushbutton telephone, you can still use them if you know what the exchange was for your area. In NYC the exchanges occasionally, but not frequently, stood for the neighborhoods in which they applied, such as on this sign, located at the BAyside Long Island Rail Road building at the car service adjoining it.
A full list of former NYC telephone exchanges can be found here.
8/28/15