The local number routing (LRN) technique
Number portability has made it possible to switch service providers.
Area code 020 is London. Due to the introduction of number portability, it is no longer possible to reliably pinpoint a neighborhood by the first few digits of the local number.
mobile number portability
The practice is called Local Number Portability. Hence the name, you can't use it if the number would not be local (i.e. if it is in a different area code from you when you want to switch carriers).
There is no area code 0208 in the UK. The area code for London is just 020, with 8-digit local numbers. A number beginning with 020 8749 is most likely a BT landline in Shepherds Bush, but with number portability any specific 020 number could be located anywhere in London, served by any local phone company.
A UK telephone number beginning 0141 946 is most likely a BT landline in Maryhill, Glasgow. However, with number portability, any 0141 number could be located anywhere in the Glasgow area, served by any local telephone company.
Glasgow is area code 0141, and a number beginning 0141 424 is most likely a BT landline in Pollok, but number portability means that you can no longer tell what part of the city by the first few digits of the local number.
The 360-473 prefix is in Bremerton, Washington. There's no way to know if a particular number is a cell phone or a landline. Local number portability means that you can change from a cell phone to a landline, or vice-versa, and keep the same number.
In the UK, telephone area code 020 is London. A number beginning with 020 3432 is a "virtual" number that could be anywhere in London. Furthermore, with number portability any specific 020 number could be located anywhere in the London area, served by any local phone company.
Area code 020 is London. A number beginning 020 8674 is most likely a BT landline in Tulse Hill; however, with number portability, any 020 number could be located anywhere in London, served by any local phone company.
Glasgow is area code 0141, or +44 141 in international format. A number beginning 0141 551 is most likely a BT landline in Bridgeton. However, due to number portability, it is not reliably possible to narrow down a number to a neighborhood based on the first few digits of the local number.