How can you explain that Cardiff's area code is 029 and not 02920?

Answer 1

Simplest is to explain how area codes and local dialling work:

• In the United Kingdom, landline phones have local numbers which can be used to dial within the area. These are normally 6 to 8 digits long, although they can sometimes be even shorter.
• Area codes form part of the full national number needed when dialling from outside the area or from a mobile phone. It is the part of the number that you do not need to dial when calling locally.

Within the Cardiff (029) area, all local calls are dialable using a full eight digit number, such as 20878889. The part which is optional is the 029, which proves that 029 is the code.

If the code was 02920, then local calls would be diallable using just the last 6 digits (such as 878889) - but this is not possible, therefore the code cannot be 02920 as the '20' is not optional. Furthermore, there are now also numbers in the range (029) 21xx xxxx.

As Cardiff had six-digit local numbers before the year 2000, and as most numbers started with '20' at first, writing '02920' is a common mistake and can cause confusion. It is helpful to write Cardiff numbers in the correct (029) xxxx xxxx format, as this makes clear what the area code is and assists people trying to dial locally.