Ottawa has two telephone area codes: the original code, 613, and the newer area code, 343. The second area code was added in 2010 due to high demand for numbers, according to Canada.com.
The country calling code for Canada is +1. If calling a number in Ottawa from outside Canada, it should be preceded by the country code, notes Country Code. For international calls to Canada, dial the full area code, +1-613 or +1-343, followed by the number of the telephone being called.
The 343 area code was added after the supply of 613 phone numbers grew close to being exhausted.