Editing Seven-digit dialing (section)

===1960 to 1981===
Major progress may be noted in provisioning DDD service. Long-distance billing was computerized in the 1960s to the early 1980s. Few area codes were introduced during this time. [[Toll-free telephone number|Toll-free]] 800-service was introduced. Service demands in the largest American cities of New York and greater Los Angeles area resulted in the first use of interchangeable central office codes (NXX). All-number calling was implemented, replacing 2L-5N telephone numbers. A very small number of places still did not use a seven-digit numbering plan by 1981.