Telephone numbering plan

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"Area Codes" redirects here. Telephone numbering plan_sentence_0

For the Ludacris song, see Area Codes (song). Telephone numbering plan_sentence_1

A telephone numbering plan is a type of numbering scheme used in telecommunication to assign telephone numbers to subscriber telephones or other telephony endpoints. Telephone numbering plan_sentence_2

Telephone numbers are the addresses of participants in a telephone network, reachable by a system of destination code routing. Telephone numbering plan_sentence_3

Telephone numbering plans are defined in each of administrative regions of the public switched telephone network (PSTN) and they are also present in private telephone networks. Telephone numbering plan_sentence_4

For public number systems, geographic location plays a role in the sequence of numbers assigned to each telephone subscriber. Telephone numbering plan_sentence_5

Many numbering plans subdivide their territory of service into geographic regions designated by a prefix, often called an area code or city code, which is a set of digits forming the most-significant part of the dialing sequence to reach a telephone subscriber. Telephone numbering plan_sentence_6

Numbering plans may follow a variety of design strategies which have often arisen from the historical evolution of individual telephone networks and local requirements. Telephone numbering plan_sentence_7

A broad division is commonly recognized between closed numbering plans, such as found in North America, which feature fixed-length area codes and local numbers, while open numbering plans feature a variance in the length of the area code, local number, or both of a telephone number assigned to a subscriber line. Telephone numbering plan_sentence_8

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. Telephone numbering plan_sentence_9

It is an open numbering plan, however, imposing a maximum length of 15 digits to telephone numbers. Telephone numbering plan_sentence_10

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 numbering plan_sentence_11

Private numbering plans exist in telephone networks that are privately operated in an enterprise or organizational campus. Telephone numbering plan_sentence_12

Such systems may be supported by a private branch exchange (PBX), which provides a central access point to the PSTN and also controls internal calls between telephone extensions. Telephone numbering plan_sentence_13

In contrast to numbering plans, which determine telephone numbers assigned to subscriber stations, dialing plans establish the customer dialing procedures, i.e., the sequence of digits or symbols to be dialed to reach a destination. Telephone numbering plan_sentence_14

It is the manner in which the numbering plan is used. Telephone numbering plan_sentence_15

Even in closed numbering plans, it is not always necessary to dial all digits of a number. Telephone numbering plan_sentence_16

For example, an area code may often be omitted when the destination is in the same area as the calling station. Telephone numbering plan_sentence_17

Number structure Telephone numbering plan_section_0

Most national telephone administrations have enacted numbering plans that conform to the international standard E.164. Telephone numbering plan_sentence_18

E.164 conformant telephone numbers consist of a country calling code and a national telephone number. Telephone numbering plan_sentence_19

National telephone numbers are defined by national or regional numbering plans, such as the European Telephony Numbering Space, the North American Numbering Plan (NANP), or the UK number plan. Telephone numbering plan_sentence_20

Within the national numbering plan, a complete destination telephone number is composed of an area code and a subscriber telephone number. Telephone numbering plan_sentence_21

The subscriber number is the number assigned to a line connected to customer equipment. Telephone numbering plan_sentence_22

The first few digits of the subscriber number may indicate smaller geographical areas or individual telephone exchanges. Telephone numbering plan_sentence_23

In mobile networks they may indicate the network provider. Telephone numbering plan_sentence_24

Callers in a given area or country sometimes do not need to include the particular area prefixes when dialing within the same area. Telephone numbering plan_sentence_25

Devices that dial telephone numbers automatically may include the full number with area and access codes. Telephone numbering plan_sentence_26

Country code Telephone numbering plan_section_1

Country codes are necessary only when dialing telephone numbers in other countries than the originating telephone. Telephone numbering plan_sentence_27

These are dialed before the national telephone number. Telephone numbering plan_sentence_28

By convention, international telephone numbers are indicated in listings by prefixing the country code with a plus sign (+). Telephone numbering plan_sentence_29

This reminds the subscriber to dial the international dialing prefix in the country from which the call is placed. Telephone numbering plan_sentence_30

For example, the international dialing prefix or access code in all NANP countries is 011, while it is 00 in most European countries. Telephone numbering plan_sentence_31

In some GSM networks, it may be possible to dial +, which may be recognized automatically by the network carrier in place of the international access code. Telephone numbering plan_sentence_32

Area code Telephone numbering plan_section_2

Many telephone numbering plans are structured based on divisions into geographic areas of the service territory. Telephone numbering plan_sentence_33

Each area identified in the plan is assigned a numeric routing code. Telephone numbering plan_sentence_34

This concept was first developed for Operator Toll Dialing of the Bell System in the early 1940s, which preceded the North American Numbering Plan of 1947. Telephone numbering plan_sentence_35

The North American Numbering Plan (NANP) divided the North American service territories into numbering plan areas (NPAs), and assigned to each NPA a unique numerical prefix, the numbering plan area code, which became known in short-form as area code. Telephone numbering plan_sentence_36

The area code is prefixed to each telephone number issued in its service area. Telephone numbering plan_sentence_37

National telecommunication authorities use various formats and dialing rules for area codes. Telephone numbering plan_sentence_38

The size of area code prefixes may either be fixed or variable. Telephone numbering plan_sentence_39

Area codes in the NANP have three digits, while two digits are used in Brazil, one digit in Australia and New Zealand. Telephone numbering plan_sentence_40

Variable-length formats exist in multiple countries including: Argentina, Austria (1 to 4), Germany (2 to 5 digits), Japan (1 to 5), Mexico (2 or 3 digits), Peru (1 or 2), Syria (1 or 2) and the United Kingdom. Telephone numbering plan_sentence_41

In addition to digit count, the format may be restricted to certain digit patterns. Telephone numbering plan_sentence_42

For example, the NANP had at times specific restrictions on the range of digits for the three positions, and required assignment to geographical areas avoiding nearby areas receiving similar area codes to avoid confusion and misdialing. Telephone numbering plan_sentence_43

Some countries, such as Uruguay, have merged variable-length area codes and telephone numbers into fixed-length numbers that must always be dialed independently of location. Telephone numbering plan_sentence_44

In such administrations, the area code is not distinguished formally in the telephone number. Telephone numbering plan_sentence_45

In the UK, area codes were first known as subscriber trunk dialling (STD) codes. Telephone numbering plan_sentence_46

Depending on local dialing plans, they are often necessary only when dialed from outside the code area or from mobile phones. Telephone numbering plan_sentence_47

In North America ten-digit dialing is required in areas with overlay plans. Telephone numbering plan_sentence_48

The strict correlation of a telephone to a geographical area has been broken by technical advances, such as local number portability and Voice over IP service. Telephone numbering plan_sentence_49

When dialing a telephone number, the area code may be preceded by a trunk prefix (national access code), the international access code and country code. Telephone numbering plan_sentence_50

Area codes are often quoted by including the national access code. Telephone numbering plan_sentence_51

For example, a number in London may be listed as 020 7946 0321. Telephone numbering plan_sentence_52

Users must correctly interpret 020 as the code for London. Telephone numbering plan_sentence_53

If they call from another station within London, they may merely dial 7946 0321, or if dialing from another country, the initial 0 should be omitted after the country code. Telephone numbering plan_sentence_54

Subscriber dialing procedures Telephone numbering plan_section_3

A dial plan establishes the expected sequence of digits dialed on subscriber premises equipment, such as telephones, in private branch exchange (PBX) systems, or in other telephone switches to effect access to the telephone networks for the routing of telephone calls, or to effect or activate specific service features by the local telephone company, such as 311 or 411 service. Telephone numbering plan_sentence_55

A variety of dial plans may exist within a numbering plan and these often depend on the network architecture of the local telephone operating company. Telephone numbering plan_sentence_56

Variable-length dialing Telephone numbering plan_section_4

Within the North American Numbering Plan (NANP), the administration defines standard and permissive dialing plans, specifying the number of mandatory digits to be dialed for local calls within the area code, as well as alternate, optional sequences, such as adding the prefix 1 before the telephone number. Telephone numbering plan_sentence_57

Despite the closed numbering plan in the NANP, different dialing procedures exist in many of the territories for local and long-distance telephone calls. Telephone numbering plan_sentence_58

This means that to call another number within the same city or area, callers need to dial only a subset of the full telephone number. Telephone numbering plan_sentence_59

For example, in the NANP, only the seven-digit number may need to be dialed, but for calls outside the local numbering plan area, the full number including the area code is required. Telephone numbering plan_sentence_60

In these situations, ITU-T Recommendation E.123 suggests to list the area code in parentheses, signifying that in some cases the area code is optional or may not be required. Telephone numbering plan_sentence_61

Internationally, an area code is typically prefixed by a domestic trunk access code (usually 0) when dialing from inside a country, but is not necessary when calling from other countries; there are exceptions, such as for Italian land lines. Telephone numbering plan_sentence_62

To call a number in Sydney, Australia, for example: Telephone numbering plan_sentence_63

Telephone numbering plan_unordered_list_0

The plus character (+) in the markup signifies that the following digits are the country code, in this case 61. Telephone numbering plan_sentence_64

Some phones, especially mobile telephones, allow the + to be entered directly. Telephone numbering plan_sentence_65

For other devices the user must replace the + with the international access code for their current location. Telephone numbering plan_sentence_66

In the United States, most carriers require the caller to dial 011 before the destination country code. Telephone numbering plan_sentence_67

New Zealand has a special-case dial plan. Telephone numbering plan_sentence_68

While most nations require the area code to be dialed only if it is different, in New Zealand, one needs to dial the area code if the phone is outside the local calling area. Telephone numbering plan_sentence_69

For example, the town of Waikouaiti is in the Dunedin City Council jurisdiction, and has phone numbers (03) 465 7xxx. Telephone numbering plan_sentence_70

To call the city council in central Dunedin (03) 477 4000, residents must dial the number in full, including the area code, even though the area code is the same, as Waikouaiti and Dunedin lie in different local calling areas (Palmerston and Dunedin, respectively.) Telephone numbering plan_sentence_71

In many areas of the NANP, the domestic trunk code (long-distance access code) must also be dialed along with the area code for long-distance calls even within the same numbering plan area. Telephone numbering plan_sentence_72

For example, to call a number in Regina in area code 306 (Regina and the rest of the province of Saskatchewan are also served by the overlay code 639): Telephone numbering plan_sentence_73

Telephone numbering plan_unordered_list_1

  • 306 xxx xxxx — within Regina, Lumsden and other local areasTelephone numbering plan_item_1_3
  • 1 306 xxx xxxx — within Saskatchewan, but not within the Regina local calling area, e.g., SaskatoonTelephone numbering plan_item_1_4
  • 1 306 xxx xxxx — anywhere within the NANP outside SaskatchewanTelephone numbering plan_item_1_5

In many parts of North America, especially in area code overlay plans, dialing the area code, or 1 and the area code, is required even for local calls. Telephone numbering plan_sentence_74

Dialing from mobile phones does not require the trunk code in the US, although it is still necessary for calling all long-distance numbers from a mobile phone in Canada. Telephone numbering plan_sentence_75

Many mobile handsets automatically add the area code of the set's telephone number for outbound calls, if not dialed by the user. Telephone numbering plan_sentence_76

In some parts of the United States, especially northeastern states such as Pennsylvania served by Verizon Communications, the ten-digit number must be dialed. Telephone numbering plan_sentence_77

If the call is not local, the call fails unless the dialed number is preceded by digit 1. Telephone numbering plan_sentence_78

Thus: Telephone numbering plan_sentence_79

Telephone numbering plan_unordered_list_2

  • 610 xxx xxxx — local calls within the 610 area code and its overlay (484), as well as calls to or from the neighboring 215 area code and its overlay, 267. Area code is required; one of two completion options for mobile phones within the U.S.Telephone numbering plan_item_2_6
  • 1 610 xxx xxxx — calls from numbers outside the 610/484 and 215/267 area codes; second of two completion options for mobile phones within the U.S.Telephone numbering plan_item_2_7

In California and New York, because of the existence of both overlay area codes (where an area code must be dialed for every call) and non-overlay area codes (where an area code is dialed only for calls outside the subscriber's home area code), "permissive home area code dialing" of 1 + the area code within the same area code, even if no area code is required, has been permitted since the mid-2000s. Telephone numbering plan_sentence_80

For example, in the 559 area code (a non-overlay area code), calls may be dialed as 7 digits (XXX-XXXX) or 1-559 + 7 digits. Telephone numbering plan_sentence_81

The manner in which a call is dialed does not affect the billing of the call. Telephone numbering plan_sentence_82

This "permissive home area code dialing" helps maintain uniformity and eliminates confusion given the different types of area code relief that has made California the nation's most "area code" intensive State. Telephone numbering plan_sentence_83

Unlike other states with overlay area codes (Texas, Maryland, Florida and Pennsylvania and others), the California Public Utilities Commission and the New York State Public Service Commission maintain two different dial plans: Landlines must dial 1 + area code whenever an Area Code is part of the dialed digits while cellphone users can omit the "1" and just dial 10 digits. Telephone numbering plan_sentence_84

Many organizations have private branch exchange systems which permit dialing the access digit(s) for an outside line (usually 9 or 8), a "1" and finally the local area code and xxx xxxx in areas without overlays. Telephone numbering plan_sentence_85

This aspect is unintentionally helpful for employees who reside in one area code and work in an area code with one, two, or three adjacent area codes. Telephone numbering plan_sentence_86

1+ dialing to any area code by an employee can be done quickly, with all exceptions processed by the private branch exchange and passed onto the public switched telephone network. Telephone numbering plan_sentence_87

Full-number dialing Telephone numbering plan_section_5

In small countries or areas, the full telephone number is used for all calls, even in the same area. Telephone numbering plan_sentence_88

This has traditionally been the case in small countries and territories where area codes have not been required. Telephone numbering plan_sentence_89

However, there has been a trend in many countries towards making all numbers a standard length, and incorporating the area code into the subscriber's number. Telephone numbering plan_sentence_90

This usually makes the use of a trunk code obsolete. Telephone numbering plan_sentence_91

For example, to call someone in Oslo in Norway before 1992, it was necessary to dial: Telephone numbering plan_sentence_92

Telephone numbering plan_unordered_list_3

  • xxx xxx (within Oslo - no area code required)Telephone numbering plan_item_3_8
  • (02) xxx xxx (within Norway - outside Oslo)Telephone numbering plan_item_3_9
  • +47 2 xxx xxx (outside Norway)Telephone numbering plan_item_3_10

After 1992, this changed to a closed eight-digit numbering plan, e.g.: Telephone numbering plan_sentence_93

Telephone numbering plan_unordered_list_4

  • 22xx xxxx (within Norway - including Oslo)Telephone numbering plan_item_4_11
  • +47 22xx xxxx (outside Norway)Telephone numbering plan_item_4_12

However, in other countries, such as France, Belgium, Japan, Switzerland, South Africa and some parts of North America, the trunk code is retained for domestic calls, whether local or national, e.g., Telephone numbering plan_sentence_94

Telephone numbering plan_unordered_list_5

  • Paris 01 xx xx xx xx (outside France +33 1 xxxx xxxx)Telephone numbering plan_item_5_13
  • Brussels 02 xxx xxxx (outside Belgium +32 2 xxx xxxx)Telephone numbering plan_item_5_14
  • Geneva 022 xxx xxxx (outside Switzerland +41 22 xxx xxxx)Telephone numbering plan_item_5_15
  • Cape Town 021 xxx xxxx (outside South Africa +27 21 xxx xxxx)Telephone numbering plan_item_5_16
  • New York 1 212 xxx xxxx (outside the North American Numbering Plan +1 212 xxx xxxx)Telephone numbering plan_item_5_17
  • Fukuoka 092 xxx xxxx (outside the Japanese Numbering Plan +81 92 xxx xxxx)Telephone numbering plan_item_5_18
  • India "0-10 Digit Number" (outside India +91 XXXXXXXXXX). In India due to the availability of multiple operators, the metro cities have short codes which range from 2 to 8 digits.Telephone numbering plan_item_5_19

While some, like Italy, require the initial zero to be dialed, even for calls from outside the country, e.g., Telephone numbering plan_sentence_95

Telephone numbering plan_unordered_list_6

  • Rome 06 xxxxxxxx (outside Italy +39 06 xxxxxxxx)Telephone numbering plan_item_6_20

While dialing of full national numbers takes longer than a local number without the area code, the increased use of phones that can store numbers means that this is of decreasing importance. Telephone numbering plan_sentence_96

It also makes it easier to display numbers in the international format, as no trunk code is required—hence a number in Prague, Czech Republic, can now be displayed as: Telephone numbering plan_sentence_97

Telephone numbering plan_unordered_list_7

  • 2xx xxx xxx (inside Czech Republic)Telephone numbering plan_item_7_21
  • +420 2xx xxx xxx (outside Czech Republic)Telephone numbering plan_item_7_22

as opposed to before September 21, 2002: Telephone numbering plan_sentence_98

Telephone numbering plan_unordered_list_8

  • 02 / xx xx xx xx (inside Czech Republic)Telephone numbering plan_item_8_23
  • +420 2 / xx xx xx xx (outside Czech Republic)Telephone numbering plan_item_8_24

Some countries already switched, but trunk prefix re-added with the closed dialing plan, for example in Bangkok, Thailand before 1997: Telephone numbering plan_sentence_99

Telephone numbering plan_unordered_list_9

  • xxx-xxxx (inside Bangkok)Telephone numbering plan_item_9_25
  • 02-xxx-xxxx (inside Thailand)Telephone numbering plan_item_9_26
  • +66 2-xxx-xxxx (outside Thailand)Telephone numbering plan_item_9_27

This was changed in 1997: Telephone numbering plan_sentence_100

Telephone numbering plan_unordered_list_10

  • 2-xxx-xxxx (inside Thailand)Telephone numbering plan_item_10_28
  • +66 2-xxx-xxxx (outside Thailand)Telephone numbering plan_item_10_29

Trunk prefix was re-added in 2001 Telephone numbering plan_sentence_101

Telephone numbering plan_unordered_list_11

  • 02-xxx-xxxx (inside Thailand)Telephone numbering plan_item_11_30
  • +66 2-xxx-xxxx (outside Thailand)Telephone numbering plan_item_11_31

International numbering plan Telephone numbering plan_section_6

The E.164 standard of the International Telecommunications Union is an international numbering plan and establishes a country calling code (country code) for each member organization. Telephone numbering plan_sentence_102

Country codes are prefixes to national telephone numbers that denote call routing to the network of a subordinate number plan administration, typically a country, or group of countries with a uniform numbering plan, such as the NANP. Telephone numbering plan_sentence_103

E.164 permits a maximum length of 15 digits for the complete international phone number consisting of the country code, the national routing code (area code), and the subscriber number. Telephone numbering plan_sentence_104

E.164 does not define regional numbering plans, however, it does provide recommendations for new implementations and uniform representation of all telephone numbers. Telephone numbering plan_sentence_105

Within the system of country calling codes, the ITU has defined certain prefixes for special services and assigns such codes for independent international networks, such as satellite systems, spanning beyond the scope of regional authorities. Telephone numbering plan_sentence_106

Satellite telephone systems Telephone numbering plan_section_7

Satellite phones are usually issued with numbers with a special country calling code. Telephone numbering plan_sentence_107

For example, Inmarsat satellite phones are issued with code +870, while Global Mobile Satellite System providers, such as Iridium, issue numbers in country code +881 ("Global Mobile Satellite System") or +882 ("International Networks"). Telephone numbering plan_sentence_108

Some satellite phones are issued with ordinary phone numbers, such as Globalstar satellite phones issued with NANP telephone numbers. Telephone numbering plan_sentence_109

Telephone numbering plan_unordered_list_12

  • Inmarsat: +870: SNAC (Single Network Access Code)Telephone numbering plan_item_12_32
  • ICO Global: +881 0, +881 1Telephone numbering plan_item_12_33
  • Ellipso: +881 2, +881 3Telephone numbering plan_item_12_34
  • Iridium: +881 6, +881 7Telephone numbering plan_item_12_35
  • Globalstar: +881 8, +881 9Telephone numbering plan_item_12_36
  • Emsat: +882 13Telephone numbering plan_item_12_37
  • Thuraya: +882 16Telephone numbering plan_item_12_38
  • ACeS: +882 20Telephone numbering plan_item_12_39

+ 88184 Telephone numbering plan_sentence_110

Special services Telephone numbering plan_section_8

Some country calling codes are issued for special services, or for international/inter regional zones. Telephone numbering plan_sentence_111

Telephone numbering plan_unordered_list_13

  • +388 5 – shared code for groups of nationsTelephone numbering plan_item_13_40
  • +388 3 – European Telephony Numbering Space – Europe-wide services (discontinued)Telephone numbering plan_item_13_41
  • +800 – International Freephone (UIFN)Telephone numbering plan_item_13_42
  • +808 – reserved for Shared Cost ServicesTelephone numbering plan_item_13_43
  • +878 – Universal Personal Telecommunications servicesTelephone numbering plan_item_13_44
  • +881 – Global Mobile Satellite SystemTelephone numbering plan_item_13_45
  • +882 and +883 – International NetworksTelephone numbering plan_item_13_46
  • +888 - international disaster relief operationsTelephone numbering plan_item_13_47
  • +979 – International Premium Rate ServiceTelephone numbering plan_item_13_48
  • +991 – International Telecommunications Public Correspondence Service trial (ITPCS)Telephone numbering plan_item_13_49
  • +999 – reserved for future global serviceTelephone numbering plan_item_13_50

Numbering plan indicator Telephone numbering plan_section_9

The numbering plan indicator (NPI) is a number which is defined in the ITU standard Q.713, paragraph, indicating the numbering plan of the attached telephone number. Telephone numbering plan_sentence_112

NPIs can be found in Signalling Connection Control Part (SCCP) and short message service (SMS) messages. Telephone numbering plan_sentence_113

As of 2004, the following numbering plans and their respective numbering plan indicator values have been defined: Telephone numbering plan_sentence_114

Telephone numbering plan_table_general_0

NPITelephone numbering plan_header_cell_0_0_0 DescriptionTelephone numbering plan_header_cell_0_0_1 StandardTelephone numbering plan_header_cell_0_0_2
0Telephone numbering plan_cell_0_1_0 unknownTelephone numbering plan_cell_0_1_1 Telephone numbering plan_cell_0_1_2
1Telephone numbering plan_cell_0_2_0 ISDN TelephonyTelephone numbering plan_cell_0_2_1 E.164Telephone numbering plan_cell_0_2_2
2Telephone numbering plan_cell_0_3_0 genericTelephone numbering plan_cell_0_3_1 Telephone numbering plan_cell_0_3_2
3Telephone numbering plan_cell_0_4_0 dataTelephone numbering plan_cell_0_4_1 X.121Telephone numbering plan_cell_0_4_2
4Telephone numbering plan_cell_0_5_0 telexTelephone numbering plan_cell_0_5_1 F69Telephone numbering plan_cell_0_5_2
5Telephone numbering plan_cell_0_6_0 maritime mobileTelephone numbering plan_cell_0_6_1 E.210 and E.211Telephone numbering plan_cell_0_6_2
6Telephone numbering plan_cell_0_7_0 land mobileTelephone numbering plan_cell_0_7_1 E.212Telephone numbering plan_cell_0_7_2
7Telephone numbering plan_cell_0_8_0 ISDN/mobileTelephone numbering plan_cell_0_8_1 E.214Telephone numbering plan_cell_0_8_2

Private numbering plan Telephone numbering plan_section_10

Like a public telecommunications network, a private telephone network in an enterprise or within an organizational campus may implement a private numbering plan for the installed base of telephones for internal communication. Telephone numbering plan_sentence_115

Such networks operate a private switching system or a private branch exchange (PBX) within the network. Telephone numbering plan_sentence_116

The internal numbers assigned are often called extension numbers, as the internal numbering plan extends an official, published main access number for the entire network. Telephone numbering plan_sentence_117

A caller from within the network only dials the extension number assigned to another internal destination telephone. Telephone numbering plan_sentence_118

A private numbering plan provides the convenience of mapping station telephone numbers to other commonly used numbering schemes in an enterprise. Telephone numbering plan_sentence_119

For example, station numbers may be assigned as the room number of a hotel or hospital. Telephone numbering plan_sentence_120

Station numbers may also be strategically mapped to certain keywords composed from the letters on the telephone dial, such as 4357 (help) to reach a help desk. Telephone numbering plan_sentence_121

The internal number assignments may be independent of any direct inward dialing (DID) services provided by external telecommunication vendors. Telephone numbering plan_sentence_122

For numbers without DID access, the internal switch relays externally originated calls via an operator, an automated attendant or an electronic interactive voice response system. Telephone numbering plan_sentence_123

Telephone numbers for users within such systems are often published by suffixing the official telephone number with the extension number, e.g., 1-800-555-0001 x2055. Telephone numbering plan_sentence_124

Some systems may automatically map a large block of DID numbers (differing only in a trailing sequence of digits) to a corresponding block of individual internal stations, allowing each of them to be reached directly from the public switched telephone network. Telephone numbering plan_sentence_125

In some of these cases, a special shorter dial-in number can be used to reach an operator who can be asked for general information, e.g. help looking up or connecting to internal numbers. Telephone numbering plan_sentence_126

For example, individual extensions at Universität des Saarlandes can be dialed directly from outside via their four-digit internal extension +49-681-302-xxxx, whereas the university's official main number is +49-681-302-0 (49 is the country code for Germany, 681 is the area code for Saarbrücken, 302 the prefix for the university). Telephone numbering plan_sentence_127

Callers within a private numbering plan often dial a trunk prefix to reach a national or international destination (outside line) or to access a leased line (or tie-line) to another location within the same enterprise. Telephone numbering plan_sentence_128

A large manufacturer with factories and offices in multiple cities may use a prefix (such as '8') followed by an internal routing code to indicate a city or location, then an individual four- or five-digit extension number at the destination site. Telephone numbering plan_sentence_129

A common trunk prefix for an outside line on North American systems is the digit 9, followed by the outside destination number. Telephone numbering plan_sentence_130

Additional dial plan customisations, such as single-digit access to a hotel front desk or room service from an individual room, are available at the sole discretion of the PBX owner. Telephone numbering plan_sentence_131

See also Telephone numbering plan_section_11

Telephone numbering plan_unordered_list_14

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: numbering plan.