The calling code for each country. A calling code should not be confused with an area or city code. For instance, the calling code for the United States is 1, and the area code for Detroit is 313. In order to dial Detroit from overseas you must dial the 1, plus 313, then the actual phone number. It's also common to see a “+” in front of the calling code, e.g., +1 313 XXX-XXXX.