The full number will be (020) 7890 xxxx.
The London Area Code is (020).
The Exchange will be identified by the '7890' part.
It is Victoria / Westminster / South Kensington area in the SW1 / E1 postcode areas.
In the United Kingdom, 020 is the area code allocated to London. It covers a large area, including central London, most of the outer boroughs and small parts of some neighbouring counties.
The 020 prefix is used primarily for the city's fixed, landline phone service, with mobile phones and pagers usually using a separate, nationwide range of numbers beginning with 07. This is standard practice in most of Europe, where mobile phones are charged at a different rate to standard landline phone calls and accordingly are not assigned geographic area codes.
About London phone numbers
The 020 code has existed since April 2000, when it replaced two separate area codes for inner and outer London (0171 and 0181).
An 020 area code is always followed by an eight-digit local number. When calling between two normal London (020) phone lines, the area code is optional and calls can be made using just the eight-digit local number.
Occasionally, people will mistakenly refer to '0207' and '0208' codes, despite neither ever having been an area code for London. For example, (0171) 222 1234 was renumbered to (020) 7222 1234 (shorter area code, longer local number) during the year 2000, but may be incorrectly quoted as (0207) 222 1234 by individuals who are more familiar with the old way of writing London phone numbers.
Location of individual numbers
Although telephone numbers can be moved between locations and operators, it is sometimes possible to get an idea of where a London phone number was originally allocated to by looking at the first four digits after the (020) area code. For example, numbers beginning (020) 7928 are allocated to BT's Waterloo telephone exchange. Some websites provide lookup facilities.
Specific London number blocks asked about by Answers.com users previously include:
(020) 3035 xxxx - Telephone company "Plus Telecom"
(020) 3286 xxxx - Telephone company "Cable and Wireless"
(020) 3301 xxxx - Telephone company "Frontier Systems"
(020) 3511 xxxx - Telephone company "Unitel Communications"
(020) 7222 xxxx - Westminster (BT)
(020) 7233 xxxx - Westminster (BT)
(020) 7247 xxxx - Bishopsgate (BT)
(020) 7277 xxxx - Walworth, Bermondsey and New Cross (BT)
(020) 7253 xxxx - Clerkenwell (BT)
(020) 7388 xxxx - Euston (BT)
(020) 7511 xxxx - Albert Dock (BT)
(020) 7580 xxxx - Bloomsbury (BT)
(020) 7890 xxxx - Telephone company "Verizon"
(020) 8638 xxxx - Telephone company "Wavecrest"
(020) 8783 xxxx - Molesey (BT)
(020) 8853 xxxx - Greenwich (BT)
(020) 8861 xxxx - Harrow (BT)
(020) 8955 xxxx - Various north west London exchanges (BT)
It's in London - indicated by the first three digits 020. Although a quick search on the BT website returned no information for 02073.
In the UK, area code 020 (or +44 20) is London.
In the Netherlands, area code 020 (or +31 20) is Amsterdam.
Several other countries have area code 020 or codes beginning with 020.
(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
London is area code 020.
UK area code 020 is London.
A UK telephone number like (020) 84xx xxxx will be in London. You need to state two more digits in order to be able to work out which part of London; eg. (020) 8484 or (020) 8411 etc.
UK area code 020 is London, but there are no valid numbers beginning with 020 4, much less 020 43. Also, the area code for London is just 020, not 020x or 020xx. There are no other UK telephone area codes beginning with 020.
020 is London. 020-3 numbers can be anywhere in London. The operator who "owns" this number is Frontier Systems. Note that the area code for London is just 020, not 0203 or 0207 or 0208.
In the UK, area code 020 is London. A number beginning with 020 8488 could be located anywhere in the 020 London area. It is not possible to specify the location more specifically.
UK telephone area code 020 is London and surrounding areas. It is not possible to narrow down the location any further with the information given. Furthermore, with number portability, any specific 020 number could be located anywhere in the greater London 020 area.
Area code 020 is London. There is no more specific geographic information possible from the information in your question.
Bromley is covered by the area code for London, which is 020.
In the UK, area code 020 is for landlines in London. 84 would be the first two digits of an eight-digit local number.
In the UK, area code 020 is London. There is no area code 0208.
UK telephone area code 020 is London, including both the former "Inner London" and "Outer London" zones. A number beginning with 020 7485 is most likely a BT landline in Kentish Town, but with number portability any particular 020 number could be located anywhere in the greater London 020 zone, served by any local telephone company.