system
Context: Telephone numbers in the United Kingdom are administered by the UK government's Office of Communications (Ofcom). For this purpose Ofcom established a telephone numbering plan, known as the "National Telephone Numbering Plan", which is the system for assigning telephone numbers to subscriber stations. Since 28 April 2001, almost all geographic numbers and most non-geographic numbers have 9 or 10 national (significant) numbers after the "0" trunk code. All mobile telephone numbers have 10 national (significant) numbers after the "0" trunk code. The overall structure of the UK's National Numbering Plan is: A short sample of geographic numbers, set out in the officially approved (Ofcom) number groups: In the United Kingdom, area codes are two, three, four, or, rarely, five digits long (after the initial zero). Regions with shorter area codes, typically large cities, permit the allocation of more telephone numbers as the local number portion has more digits. Local customer numbers are four to eight figures long. The total number of digits is ten, but in a very few areas the total may be nine digits (after the initial zero). The "area code" is also referred to as an "STD (code)" (subscriber trunk dialling) or a "dialling code" in the UK.
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Who is responsible for phone numbers in the UK?
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the UK government's Office of Communications
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How is  the office's name abbreviated?
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Ofcom
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What did they establish to assign numbers?
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the "National Telephone Numbering Plan",
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What is the first digit in UK phone numbers?
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0
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What's this called?
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a trunk code
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How many digits follow it?
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9 or 10 (significant) numbers
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How many for mobile phones?
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10
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What is the overall structure of the plan?
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A short sample of geographic numbers, set out in the officially approved (Ofcom) number groups
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How long are area codes?
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from two to 5 digits
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Where are shorter ones usually found?
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large cities
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What  do they have more of?
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telephone numbers
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How long are local customer numbers?
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four to eight figures long
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How long is the total amount of digits?
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generally ten
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Is it ever different?
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Yes
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What's another term for the area  code?
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STD code
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Any others?
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Yes
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What?
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a "dialling code"
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Since what date has this system been in place?
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28 April 2001