The International Telecommunication Union has recommended the number 00 as the international access code. It has also been implemented by most countries.
The international access code is entered before the country code. So, if a German phone number is dialed from the USA, the international access code 00 is dialed first, followed by the country code 49 for Germany, the area code 221 for Cologne, and the subscriber number 123456. So that the complete phone number looks like this: 00 49 221 123456.