Is it better to store telephone numbers in some canonical format or “as entered”?

Question

Storing a telehone number in some kind of canonical format has several advantages from a programmers point of view, but it might confuse the user, if sudde

Answer 1

The UK is a special case as we have variable length STD (area) codes and variable length subscriber number itself. The longer the STD code the shorter the number. Germany and a few other countries also have a similar system.

Numbers are mostly 10 digits after the 0 trunk (long distance) prefix, but several dozen areas also have some 9 digit numbers.

• 020 2345 5678 (London) also Cardiff, Southampton, Portsmouth, Coventry and Northern Ireland
• 0115 234 4567 (Nottingham) also Sheffield, Bristol, Leicester, Reading and Leeds
• 0141 345 5678 (Glasgow) also Birmingham, Edinburgh, Tyneside, Manchester and Liverpool
• 01332 234 456 (Derby) most other areas (about 580 areas) also use this format
• 01750 45678 (Selkirk) and about 40 areas have some numbers that are a digit shorter
• 017687 45678 (Keswick) also Langholm, Hornby, Hawkshead, Grange-over-Sands, Sedbergh, Wigton, Raughton Head, Brampton, Appleby, Pooley Bridge and Gosforth.
• 016977 2345 (Brampton) The only place using "5+4" format.
• 07812 123 456 (mobile numbers)

Beware that 0800 numbers can be different lengths, e.g. 0800 567 1234 or 0800 234 456. The old 0500 numbers are also a digit shorter, e.g. 0500 456 456.

Additionally some people like to group their numbers 234 234 while others use 23 23 23 (depending on the actual digits).

There are arguments for storing as entered and storing in a single form:

If you store the number as just the sequence of numbers then you can output it in any way you want, either by taking into account user preferences or their locale and splitting the number up according to "rules" (what ever they may be).

If you store as entered then you'll always display it as the user expects, but you'll need to strip out non numeric values before using it, which if it's often could be expensive.