Every country has both a country calling code used to dial into a
country, and an international call prefix or international access code
used to dial out of the country. The ITU approved 00 as the general
standard some time ago, and this has been implemented by a large number
of countries, but not all.
numbers are usually written with a + before the phone number
representing the international call prefix. Some phones allow this to be
entered directly, often by holding the '0' key (most GSM mobile phones)
or with two consecutive presses of the * key, which avoids having to
know the international call prefix. For example a UK phone number
written as +44 1234 567890 would be dialed as 567890 from the '01234'
linked numbering scheme exchanges in the UK; as 01234 567890 from
elsewhere in the UK; and as 00 44 1234 567890 from countries using the
00 international access code. For countries using a prefix other than
00, simply substitute that for 00 in the last example; for example, from
North American Numbering Plan countries (including the United States and
Canada), dial 011 44 1234 567890.
Many states also provide alternative dialing arrangements for calls to
International Dialing Code: