Dialing a local number is no big deal. Dialing an international number can be quite complicated. Depending on the country you are calling, and the country that you're in, international dialing can vary quite a bit. The amount that this varies depends on the unique dialing rules of each nation.
International Access Codes and Country Codes
The first thing you need to do is figure out the international access code for the country you're in. For countries that participate in the NANP (North American Numbering Plan) the access code is "011." Participating countries includes the United States, Canada and some (but not all) Caribbean nations. It also includes all U.S. territories. For most of Europe, the access code is typically "00." The code varies from place to place in the rest of the world, though "00" is still the most prevalent. With some cell phones, you can use the "+" key to automatically dial the access code.
Once you have dialed the access code, you must then dial the country code of the nation that you are calling. There are nine "zones" within the numbering plan, and each country code within that zone starts with the number of the zone. Most nations have their own country code, with the exception of the NANP nations, which share the zone 1 code--which incidentally, is "1"--as well as Russia and Kazakhstan, which share the zone 7 code--which is of course, "7." Country codes vary in the number of digits, from one to three digits, but the first digit is always the number of the zone that country is in.
The other zones are as follows: Africa is Zone 2. Western and Eastern Europe share Zone 3 with Ireland, Central and Northern Europe share Zone 4 with the United Kingdom. South America, Mexico and the non-NANP Caribbean nations share Zone 5. Southeast Asia and Oceania share Zone 6. Zone 8 is the Far East, and Zone 9 is the Middle East.
Area Codes and Local Numbers
For the most part, dialing the area code from another country is no different from dialing the area code from within that country. However, some countries have leading zeros in their area codes that you'd only dial if you're calling internally. With these countries, when dialing from outside, you have to drop the leading zero. An example of this is the United Kingdom. When dialing London from within the U.K., you would dial (020) xxxx xxxx. From outside, you would dial +44 20 xxxx xxxx. This is actually not that different than the system used in the NANP, except because the long distance code and the country code are the same, the number is dialed the same way no matter what. A number in New York City is always 1 (212) xxx-xxxx, no matter where you are calling from.
