Why do all area codes have 3 numbers?

With new york city adding another area code 929, why 3 digits?Why do all area codes have 3 numbers?
The original area code map from 1947 was drawn when we didn't have 7 digit dialing or store and forward central offices. The idea was that there would be 3 digit area codes and 7 digit phone numbers. Notice that states with only one area code had a "0" in the second number of the area code...that's because it took longer to dial with a rotary dial! http://www.lincmad.com/map1947.html



Today's modern equipment and number portability, and the "any code" can be an area code, will probably never exhaust. If it does, they have some kind of trick that will use the second digit "9" to signify that there are more digits to follow. Something in the form of N9X.Why do all area codes have 3 numbers?
That's just the way it was originally setup back in the late 1950's. You can expect to see a change in the current numbering system in the not too distant future. It is in and has been in the planning stages for several years.Why do all area codes have 3 numbers?
//nanpa.com/ is the best source of information and resources since they're the actual ones who make those decisions.



nanpa stands for :



North American Numbering Plan Administration