International Calling

International Direct Dialing

If you want to call an international number, first you need to dial exit code or more formally international direct dialing (IDD) of origin country. In most European and all Middle East countries it's 00. Suppose that you want call a Canadian number from Iran, a country in the Middle East. The exit code in Iran is 00 and the country calling code for Canada is 1, so you need to dial 001 and then the Canadian number.

Now Imagine you want to call an Iranian number from Canada. The exit code in Canada is 011 and the country calling code for Iran is 98. So you need to dial 01198 and then the Iranian number! To avoid this type of confusion, You can replace exit code with +. So depending on origin country, + is replaced with appropriate exit code.

Knowing this type of information can be helpful in international traveling. It's always a good idea to check it in Wikipedia. The title usually is Telephone Numbers in .... For example if you google "telephone numbers in Canada, usually the first link is Wikipedia article.

Trunk Prefix

Trunk prefix is a prefix which sometimes should be dialed before area code within a country. In Canada it's 1. In UK and Iran it's 0. Usually you need to dial trunk prefix before area code, if the origin and destination of the call are in different areas but in the same country. For example the area code for Tehran Province in Iran is 21. If you are outside Tehran Province, you need to dial 021 and then the actual number. As I mentioned before check the Wikipedia article for your destination country.

E.123 Standard

It's a good idea to make yourself familiar with E.123 (standardization of phone numbers and emails. Here Canada, also in US, the format of a number is (xxx) xxx-xxxx. The three digits inside the parentheses is area code. For example 514 and 438 are area codes for Quebec Province.

When I traveled to London, I stayed in Marlin Apartments. On their website the phone number is +44(0) 20 7378 4840 which is against E.123! Let's analyze it. Suppose I want to call that number from Canada. + is replaced with 011. 44 is UK country calling code. 0 is trunk prefix in UK. 20 is area code for London and the rest is the actual number of hotel. According to E.123 you shouldn't put trunk prefix in international format, which starts with +. You must dial trunk prefix when you are in UK but outside London. It's not a valid number and it took me some time to understand that I should dial +44 20 7378 4840.