Guideline C: Respect for culture and conventions

C13: Telephone format

Allowing the customization of telephone numbers
Telephone numbers in different countries have different numbers of digits and different groupings of digits.

Guideline C13

Allow the user to customize formatting of telephone numbers.

Don't assume that international users will know the international country code for their country. Note that in some countries, telephone numbers can contain nonnumeric characters such as "1-800-IBM-4YOU". In other countries, the plus sign (+) is an integral part of the telephone number such as "+81-3-1234-5678".