Most people will never see a reason to question how and why a telephone works; it just needs to have a dial tone and someone needs to pick up when the numbers are dialed, but there is some real science behind the convention of a phone number. Let’s take a look at the codes that make up the modern day phone number.
There are 24 countries and territories that share the North American Numbering Plan (aka NANP), each of these countries has thousands if not millions of telephone users. With this many user, across so many countries the number combinations grow exponentially. As complex as this may sound, there is a rather simple science behind the coding and once understood it may help you to break down any phone number.
If you are located within the United States you may be familiar with phone numbers that look like: 1-(AAA) BBB-CCCC .It is more than probable that you have dialed that 1 before a number and did not think twice about what it meant. The fallacy with this single digit is that it meant a long-distance. This is only indirectly true. The number is actually the country code. It means that the rest on the number you are dialing is directed at a number located in NANP. This ITU country calling code excludes: Mexico, Puerto Rico, Central America, and some of the Caribbean.
The next three numbers are the area code (AAA). It is common place to understand the function of these three numbers. They are the three digits that designate a segmented geographic location to the number. However obvious their function is to most, many people do not know that in certain locations, there have been splits and overlays of area codes due to saturation of their usage. With this number we now know the city or territory.
Mobile numbers outside the US and Canada can have “area codes” which do not correspond to a geographic area. Toll-free and toll numbers have three digits placed in the “area code” section of a telephone number to assign their function. These include the prefixes 800, 877, & 900.
Next up in the number is the segment called the exchange (BBB). This second set of three digits references the original issuing service provider and type of the number. This means you can tell if the number is a landline (home) number or a mobile (cell) number. Once this is determined, you can move on to the last four numbers (CCCC), which is sometimes referred to as the station code or local number. In truth, its function is much simpler. This set of numbers is used to identify the particular subscriber (ie. the owner of the number).
Understanding the pieces, i.e. [long-distance access code]+[area code]+[exchange]+[subscriber number], will help in determining the code that lies in any NANP telephone number.