Voip Blog
Area Code Splits and Overlays
Monday, May 19, 2008
Last time, I got into how telephone numbers evolved. This time around, I'm going to get into a perennial problem as telephone usage increased: area code splits.
Reviewing from last time, we settled on 7 digit telephone numbers back in the 1960s. The first three digits of that number are considered the exchange. The first digit of the phone number can be 2 thru 9, the other two digits in the exchange can be anything.
There are some exceptions. X11 refers to special service numbers (211 used to be how you reached long distance, 411 for Directory Assistance, 911 for Emergency Services), thus they cannot be telephone prefixes. We also exclude the 555 exchange for a variety of reasons I will get into in a future post.
With that in mind, there are 791 possible exchanges in a given area code, or 7.91 million possible phone numbers. With the proliferation of phone lines in their various forms, the phone companies have had to implement either area code splits or overlays.
An area code split is taking a large area code and splitting it up, giving a new area code to another part of that area. For example, all of Washington State used to have the area code 206. In 1957, the Eastern half gained the area code 509. 206 has split again two other times since then, largely around geographical boundaries.
The other strategy that's been employed--particularly in larger metropolitan areas--is the idea of an area code overlay. This means there are two or more area codes co-exist in the same area. For example, the city of Atlanta has two area codes: 404 and 770.
The main reason overlay codes are considered problematic is that they require changes in dialing patterns. Dialing patterns, as you might have guessed, is a whole different article.
