Telephone country codes
The site country-dialing-codes.com allows you to find telephone country codes of 230 countries through the world.
For example if you try to compose a telephone number towards China, you have only to find the telephone country code correspondent, 86 in this case.
You will have next only to begin your composition by 00 followed by the indicative country (prefix 86) and next the number of the country while taking care to remove the first zero.
You can visit also International dialing codes for more informations about countries and calling phone codes, this website is in english. Otherwise you can visit codigos telefonicos for the spanish version or www.indicatifs-telephoniques.net for french version.