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A telephone number is a sequence of digits assigned to a fixed-line telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices for data transmission via the public switched telephone network (PSTN) or other private networks. Most telephone numbers are assigned to one telephone line or one mobile telephone, and most lines or mobiles have one number. A telephone number serves as an address for switching telephone calls using a system of destination routing. Telephone numbers are entered or dialed by a calling party on the originating telephone set, which transmits the sequence of digits in the process of signaling to a telephone exchange. The exchange completes the call either to another locally connected subscriber or via the PSTN to the called party. The use of telephone numbers instead of subscriber names to indicate to the telephone operator what destination line a caller wished to be connected to was developed and first used in the autumn of 1879 in Lowell, Massachusetts during a measles epidemic. Moses Greeley Parker, a local doctor, realized that if all four of the city's operators were incapacitated by the epidemic, their replacements would have great trouble quickly learning which of the switchboard's 200 jacks were assigned to which subscribers. He recommended the use of numbers instead. "The local Bell company management at first protested that its customers would consider their designation by numbers to be beneath their dignity; nevertheless, it saw the logic of the doctor's suggestion and followed it. The subscribers were not outraged; the epidemic quickly passed, but telephone numbers did not."〔Brooks, John. ''Telephone: The First Hundred Years''. Harper & Row, 1967, ISBN 0-06-010540-2: p. 74, citing "Events in Telephone History".〕 == Overview == When telephone numbers were first used they were very short, from one to three digits, and were communicated orally to a switchboard operator when initiating a call. As telephone systems have grown and interconnected to encompass worldwide communication, telephone numbers have become longer. In addition to telephones, they have been used to access other devices, such as computer modems, pagers, and fax machines. With landlines, modems and pagers falling out of use in favor of all-digital always-connected broadband Internet and mobile phones, telephone numbers are now instead taken by data-only cellular devices, such as some tablet computers, digital cameras, and even game controllers and mobile hotspots, on which it is not even possible to make or accept a phone call. The number contains the information necessary to identify uniquely the intended endpoint for the telephone call. Each such endpoint must have a unique number within the public switched telephone network. Most countries use fixed length numbers (for normal lines at least) and therefore the number of endpoints determines the necessary length of the telephone number. It is also possible for each subscriber to have a set of shorter numbers for the endpoints most often used. These "shorthand" or "speed calling" numbers are automatically translated to unique telephone numbers before the call can be connected. Some special services have their own short numbers (e.g., 1-1-9, 9-1-1,1-0-0, 0-0-0, 9-9-9, 1-1-1, and 1-1-2 being the Emergency Services numbers for China, Japan, India, South Korea, Taiwan and Sri Lanka; Canada and the United States; Australia; the United Kingdom, Ireland, South Africa, Poland, Saudi Arabia, the United Arab Emirates, Morocco, Macao, Bahrain, Qatar, Bangladesh, Botswana, Ghana, Kenya, Hong Kong, Malaysia, Mauritius, Singapore, Zimbabwe, Trinidad, Tobago; New Zealand; Kuwait and the European Union, respectively.) The dialing plan in some areas permits dialing numbers in the local calling area without using area code or city code prefixes. For example, a telephone number in North America consists of a three-digit area code, a three-digit central office code, and four digits for the line number. If the area has no area code overlays, seven-digit dialing may be permissible for calls within the area, but some areas have implemented mandatory ten-digit dialing. Other special phone numbers are used for high-capacity numbers with several telephone circuits, typically a request line to a radio station where dozens or even hundreds of callers may be trying to call in at once, such as for a contest. For each large metro area, all of these lines will share the same prefix (such as 404-741-''xxxx'' in Atlanta and 305-550-''xxxx'' in Miami), the last digits typically corresponding to the station's frequency, callsign, or moniker. In the international telephone network, the format of telephone numbers is standardized by ITU-T recommendation E.164. This specifies that the entire number should be 15 digits or shorter, and begin with a country prefix. For most countries, this is followed by an area code or city code and the subscriber number, which might consist of the code for a particular telephone exchange. ITU-T recommendation E.123 describes how to represent an international telephone number in writing or print, starting with a plus sign ("+") and the country code. When calling an international number from a landline phone, the + must be replaced with the international call prefix chosen by the country the call is being made from. Many mobile phones allow the + to be entered directly, by pressing and holding the "0" for GSM phones, or sometimes " *" for CDMA phones. The format and allocation of local phone numbers are controlled by each nation's respective government, either directly or by sponsored organizations (such as NANPA in the US or CNAC in Canada). In the United States, each state's public service commission regulates, as does the Federal Communications Commission. In Canada, which shares the same country code with the U.S. (due to Bell Canada's previous ownership by the U.S.-based Bell System), regulation is mainly through the Canadian Radio-television and Telecommunications Commission. Teleconversion is the process or act of changing one's telephone number while remaining with the same telephone company, often due to relocation. Conversely, local number portability (LNP) allows a person to move his or her existing phone number to another carrier. The two processes converge in the instance of a port-in teleconversion, where an existing number is changed to one which is brought from another carrier. This may occur where a person takes a wireline number (such as a home business) and ports it to an existing cellphone (possibly a wireless home phone), or where a new line is activated but the port-in request is still pending, the teleconversion then occurring when the porting process successfully completes. Number portability usually has geographic limitations, such as an existing local phone company only being able to port to a competitor within the same rate centre. Mobile carriers may have much larger regions called markets, which can assign or accept numbers from any area within the region; these markets vary depending on carrier. Within most North American rate centres, local wireline calls are free, while calls to all but a few nearby rate centres are considered long distance and incur a per-minute toll. In a few large US cities, as well as most points outside North America, local calls are not flat-rated or "free" by default. The world's largest toll-free calling areas are the Atlanta metropolitan area (CSA pop 6,162,195) and Greater Toronto Area (CMA pop 5,583,064) exchanges reachable locally from the respective downtown rate centres. Both span multiple area codes in some combination of split plans and overlay plans. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「telephone number」の詳細全文を読む スポンサード リンク
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