Chapter 16. Telephone Numbers
The Telecommunication Standardization Sector (ITU-T, formerly known as the International Telegraph and Telephone Consultative Committee or CCITT from the French), of the International Telecommunication Union (ITU) standardizes the international telephone number formats.
The defining standard is E.164 and its subdocuments. The numbers are up to 15 digits (excluding prefixes) and could be modeled with a regular expression that looks for a single string of digits.
The single string is not a good idea because the format is a vector encoding (see Section 03.02.06. Vector Encoding) and the components of the telephone number have meaning that can be useful. The display convention for putting punctuation separating the vector ...