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 in 1958 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. This increased the number of effectively available central office codes in each  numbering plan area (NPA) from 540 to 792, thereby staving off the threat of exhausting the number pool, which was forecast to occur by the late 20th century. History. Until the 1950s, a typical telephone number in the United States and many other countries consisted of a telephone exchange name and a four- or five-digit subscriber number. The first two or three letters of the exchange name translated into digits given by a mapping typically displayed on the telephone's rotary dial by grouping the letters around the associated digit. The table (right) shows the typical assignment in the  Bell System in use at the time. The letter Q was not used, and Z was translated to 0 (zero) on some dials, albeit never used in the name system. For example, a New Yorker's telephone number might have been CHelsea 2-5034, which a calling telephone subscriber would dial as the digit sequence 2425034, translating C to 2, and H to 4. After World War II, the newly conceived North American Numbering Plan of 1947 sought to unify all local numbering plans by using a system of two central office letters and one digit to complete the office  prefix, and four digits for line number. This system was referred to as "2L-5N", or simply "2-5". With increasing demand for telephone service in the 1950s and 1960s, resources were strained not only in employing telephone operators, and for the network system of central offices, but also for the traditional numbering plan using telephone exchange names. At first, it became necessary in some highly populated states, such as New York, to use digit combinations that could not be expressed by memorable names. The solution to the growing threat of numbering exhaustion was decided by AT&T engineers and administrators from  in-depth studies of all alternative methods. It was decided to eliminate the restrictions of using exchange or central office names. This goal had been envisioned internally within AT&T for some time. In 1954, John Karlin directed a research project that investigated the memory capacity and dialing accuracy of employees when using seven-digit telephone numbers comprising only digits. At that time, some directory publishing departments also began removing the entire central office name from telephone directories, preferring to only list the dialed letters of the prefix. The practice did not produce any adverse effects, and opened the path for  listing telephone numbers in the "2-5" style, where the two letters were unrelated to any pronounceable name. All-number calling was first field-tested in Wichita Falls, Texas in 1958 with the installation of a dial system. The results indicated a substantial reduction of dialing errors over new system installations that used the "2-5" numbering system. In small communities the new system was met with little resistance. In Council Bluffs, Iowa with c. 26,000 telephone subscribers, it also caused no major resistance in March 1960. During larger scale introductions in California in 1962, this change sparked an intense  outcry among urban users who considered all-digit dialing to be dehumanizing. Karlin, the inventor of the all-number system, stated that he had been approached by a woman at a cocktail party, "Are you the John Karlin who is responsible for all-number dialing?" He proudly replied, "Yes, I am." She then asked him, "How does it feel to be the most hated man in America?" Opponents created a variety of organizations to oppose all-number calling, including the Anti-Digit Dialing League and the Committee of Ten Million to Oppose All-Number Calling to pressure AT&T to drop  the plan. Other countries introduced similar transitions for eliminating exchange names. In the United Kingdom, the new system was known as all-figure dialling.