 All-number calling

All-number calling (ANC) is a telephone numbering plan that was introduced into the North American Numbering Plan by the Bell System in the United States starting around 1960 to replace the previous system of using a telephone exchange name as the first part of a telephone number.The plan prescribed the format of a telephone number assigned to subscriber telephones to consist of ten digits, composed from a three-digit area code, a three-digit central office code, and a four-digit station number.