Pete, the system you're referring to was common in the Bell System in that era. When Area Codes started being assigned, the local phone company would designate any suburb, including near-in suburbs, with a different Area Code in order to classify a call from the city to the "suburb" as a long distance call, and charge LD rates. Even within a city with a single Area Code, the phone company might designate some neighborhoods that were "far" from the city center as being outside the unlimited monthly calling area.