Some common international dialing codes include 44 for the United Kingdom, 33 for France, 49 for Germany, 91 for India and 89 for China. Most countries have two-digit country codes, though some, such as Ireland, have three digits. The one-digit North American dialing code, 1, is unique.
When calling an international number, callers must first enter the system exit code. This code is 00 or 011 in most countries. For instance, to call a Chinese phone number from North America, a caller has to first enter 011, then 89, and then the Chinese phone number.
Many countries write phone numbers with a zero included before the area code. International callers must remove this zero when calling into these countries. For example, to call from the United States the French number 01 40 40 XX XX, a caller enters 011 33 1 40 40 XX XX.
Phone companies use international dialing codes and system exit codes to properly route phone calls to the proper switching offices. Phone numbers serve as a map, with each section of the number directing the call to a specific switching location. Before international dialing codes were introduced, starting during the 1960s, phone operators manually switched wires on a switchboard to complete phone call circuits.