what is the maximum length of phone number
Telephone numbering plan The International Telecommunication Union (ITU) has established a comprehensive numbering plan, designated E.164, for uniform interoperability of the networks of its member state or regional administrations. It is an open numbering plan, however, imposing a maximum length of 15 digits to telephone numbers. The standard defines a country calling code (country code) for each state or region which is prefixed to each national numbering plan telephone number for international destination routing.
Telephone exchange names As demand for telephone service grew in the postâ€“World War II period, it was foreseeable that the demand would exceed the addressing capacity of the existing system of using memorable telephone central office names as prefixes in telephone numbers. Several letter combinations had no pronounceable or memorable names and could not be used. Several North American numbering plan areas (NPAs) were divided so that more office codes became available to smaller regions. However, as the growth accelerated, the Bell System decided to implement all-number calling (ANC) and to deprecate the use of central office names to provide more central office codes to each NPA. This extended the usable numbering plan and only two area code splits became necessary between 1962 and 1981. All-number calling was phased in starting in 1958 and most areas had adopted it fully by the mid-1960s. In some areas it did not become universal until the 1980s. The Bell System published and distributed area code handbooks yearly which compiled the towns available for calling using an area code.