Copyright (C) 2006-2007 Code Synthesis Tools CC Redistribution and use with or without modification are permitted under the terms of the new BSD license. See the accompanying LICENSE file. Full international telephone number is up to 15 digits long. The country code is up to 3 digits long. The area code is country-dependent and is not used for some countries. If used, it seems to be from 1 to 5 digits long. This leaves the subscriber number up to 14 digits. Plus there is the optional extension. Putting this all together, we get: country-area-subscriber-extension The area code and extension are optional. Here are a few examples: 1-800-1234567 (country-area-subscriber) 1-800-1234567-89 (country-area-subscriber-extension) 34-912345678 (country-subscriber) 34-912345678-9 (country-subscriber-extension) See also http://en.wikipedia.org/wiki/Area_code http://en.wikipedia.org/wiki/E.164 Telephone country code. Up to 3 digits long. Telephone area code. Up to 5 digits long. Telephone subscriber number. Up to 14 digits long. Telephone extension number. Theoretically of arbitrary length. Structured full international telephone number.