Telephone Numbers

Like addresses, the format for telephone numbers around the world varies significantly. Once again, input fields and the routines that process information dealing with telephone numbers should be able to handle the variety of formats.

Table 4-12 displays different formats used throughout the world.

Table 4-12 Formats for telephone numbers for selected countries.

Country	Format
China	1234 5678
France	01-23-45-67-89
Poland	(12) 345.67.89
Singapore	123 4567
Thailand	[phone] or (012) 34-5678
United Kingdom	0123 456 7890 or 01234 567890
United States	[phone]

Notice that there are different separators such as hyphens (-), periods (.), and spaces, different groupings (two, three, four, five, and six digits per group), and different numbers of total digits used (7-11). Also, the examples just given didn't include country codes, which could be anything from one to three digits.

The ITU-T standard E.164, defined by the Comit Consultatif International T l phonique et T l graphique (CCITT), states that the maximum number of digits is 15, but this doesn't include space for things like:

• "Exit" numbers for corporate telephone systems (such as, in the United States, dialing a "9" in order to place a call outside the place of business)
• Long-distance access codes
• Passwords
• Credit card numbers
• Extensions

Thus when designing and coding for display and storage of telephone numbers, do not assume one given format, but leave it very flexible. The current implementation of NLS APIs and the .NET Framework do not provide any telephone-number formatting information. Knowing this, you should:

• Keep country codes, area codes, and phone numbers in separate fields.
• Not expect a fixed number of digits for an area code or phone number. (A phone number can be anything between 4 to 11 digits.)
• Expect different separators-hyphens (-), periods (.), and commas (,)-between numbers. (You will need to do your own parsing for these separators.)