What’s up with the + symbol? What’s E.164? Do I need to include this leading zero here? How do I even make a call to another country?
If you’re like me, you never really had to really think about how phone numbers work… globally. One Wikipedia link led me to another, and I fell into the rabbit hole of phone number terminology. To get a sense of everything I was reading, I drew myself a visualization to understand all the different terms defined by the International Telecommunication Union (ITU), so I am sharing this out publicly in case anyone else also finds it useful.
Phone Number Visualized & Explained
The following example of 00 33 06 98 87 07 94 is a phone number from France broken down into its different parts.
- International prefix: this is also known as an “exit code” or an “international direct dialing (IDD) prefix”. This prefix is a set of numbers used to make a call to a phone number outside of the country you are in, typically on phones that don’t have a
+symbol available. Most people commonly don’t use the international prefix anymore, and use the+to replace it for convenience. One of these inconveniences is that the prefix itself varies from country to country (see entire list here). In the example above,00is the international prefix for France (and most European countries). However, if you were to call this French number from Canada, the number to be dialed would be011 33 06 98 87 07 94, because the international prefix for Canada is011. It is annoying to have to look up the international prefix of the country you are in before making a call, so it is preferable and much easier to just use the+symbol instead. - Country code: a set of numbers representing the country of a phone number. It comes immediately after the international prefix or the
+symbol. - National (trunk) prefix: only required in certain countries, this is a set of numbers that must be dialed before the area code when making a call within that country. For most applicable countries, the trunk prefix is typically
0, so you may see the expression “leading zero” in certain places to describe this prefix. In practice, this prefix does not need to be included when the number is called internationally, but I did include it in the visualization just for the sake of completeness, even though realistically no one would actually have that zero in there if calling from outside of France. - National (significant) number: this is the official term to represent the phone number you would typically give out casually to someone you meet in your country. I would say this is what most people believe a regular phone number is, without considering about any of the international stuff. It is composed of an area code and a subscriber number.
- Area code: a set of numbers in the national number that represents a smaller geographic area (e.g state, province, etc) in the country.
- Subscriber number: the ending set of numbers in the national number associated with the area code to uniquely identify a subscriber (i.e you).
In reality, how would I call this number if I were in France?
If you lived in France, are using a French telecom provider and wanted to call this number, you would dial the trunk prefix and then the entire national number:
06 98 87 07 94Note: France is one of those countries that require a trunk prefix, hence why the leading zero is here.
In reality, how would I call this number if I were outside of France?
If your phone has a + symbol available, you would dial, from any country, the + symbol, the country code and then the entire national number:
+33 6 98 87 07 94Note: the trunk prefix of 0 is not required here because you are calling from outside of France, so it can be dropped. However, if you do include it, it should still work.
If your phone somehow does not have a + symbol, you would dial the same number above, but removing + symbol for the international prefix of whichever country you are from.
If calling from Japan, you would dial:
010 6 98 87 07 94Because the international prefix for Japan is 010.
If calling from the United States, you would dial:
011 6 98 87 07 94Because the international prefix for the United States is 011.
Other Useful Terms
E.164 Format
This is the recommended international phone number format, also defined by the ITU, to standardize phone numbers from any country. It essentially means that a “properly” formatted international number is composed of a + symbol, the country code and then the national number, with no special characters (i.e spaces, brackets, etc). From the example above, the E.164 formatted version of that number is:
+33698870794Backend software systems should store phone numbers in this format, because it is unambiguous and provides all the necessary information about the phone number. However, the lack of spaces and special characters is not ideal for humans, so the front-end can (and should) format this to make it more readable to a user. I highly recommend using an open-source library like Google’s libphonenumber to parse, validate and format numbers.
NANP
Each country follows a specific phone numbering plan. I am including the North American Numbering Plan (NANP) here just because I have come across it myself, and because one of its terms can be easily confused with the international terms. For example, given this US number:
+1 415 678 2222- Telephone prefix: in North America, the three digits after the area code, in this case
678, is sometimes referred to as a telephone prefix (or exchange code or central office code). This prefix is not to be confused with the international prefix or the trunk prefix, despite them all having the word “prefix” in them. - Line number: in North America, the ending four digits, in this case
2222, is sometimes referred to as a line number.
Final Thoughts
Phone numbers are seemingly simple, but can get confusing if you don’t know the lingo. Hopefully this article clears some of that up. Next time you see phone numbers in your Google Meet/Zoom invites or when you’re adding someone in WhatsApp, things should be a little bit less daunting now.
