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 of them. This page lists the exceptions.
International phone numbers are usually written with a plus sign (+) before the phone number representing the international call prefix. The plus sign indicates the code required to dial out of your local area; for example, in the United Kingdom, you use 00 to dial out and 1 to call the United States with the complete format being 00-1-xxx-xxx-xxxx. 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 dialled 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 neighbouring countries.
Note: ‘~’ means to await a tone before continuing.
00
All countries not listed below.
0x0
Mauritius('x' represents one digit defining an 'International Long Distance' operating company.)
00 Works only from payphones and '+' only from mobile phones.[1]
Note that many Japanese phone subscriptions do not include international calls. If the one in use does not, you have to dial a prefix of three or four digits before the 010 prefix to select an international phone carrier. Even if your phone subscription includes international calls, you may use one of those prefixes to select a phone carrier other than the usual one. Selecting a phone carrier is mandatory if you use a public payphones. Different codes available: 001 010 (KDDI) 0033 010 (NTT) 0041 010 (Japan Telecom) 0061 010 (Japan Telecom IDC) NB: Japan Telecom and Japan Telecom IDC are different!
1xx0 ('xx' represents two-digit Chilean Carrier Selection Code; For example, an Argentinean phone number written as +54 11 23456789 would be dialed as 1230 54 1123456789 or 1880 54 1123456789)[3]
Finland, where to encourage competition between international telephone carriers, a system of prefixes beginning with 99 was introduced in addition to the 00 prefix. For example, if the subscriber dials 990-1-202-456-1111, the call will be routed to North America via TeliaSonera.
Source: How to Call International Used with permission.
* These countries are part of the North America Numbering Plan (NANP). Although they may be far from North America the country code for all NANP countries is 1; the numbers that follow are used in the same way as area codes in the U.S. and Canada.
^ This code will let the dialer choose his primary IDD carrier, usually being the telephone company he is subscribed to. A telephone line can subscribe to multiple IDD carriers in Hong Kong, and those carriers have their own international call prefix, which begins with 00 (3-4 digits), 15 (4 digits) or 16 (4 digits). See The Numbering Plan for Telecommunications Services in Hong Kong for complete code list.
^ Although in Chile all the carriers use the 1 prefix, the number of the carrier in advertising and common usage includes the 1 prefix as a part of the number.
^ The domestic call prefix 8 and international call prefix 8~10 are to be replaced by the ITU-recommended dialling prefixes of 0 and 00. The first step will be to replace area codes beginning with the digit '0' with ones beginning with '4', hence Moscow 095 becomes 495. See also Telephone numbering plan for Russia and Kazakhstan.