As telephone numbers are assigned, the availability of numbers within an area code diminishes. In order to make sure that there are always numbers available, usage is analyzed, number exhaustion dates are projected, and steps are taken to provide for more numbers.
Although short-term steps, such as “thousand block number pooling” are taken, the long-term solution is either an area code split or an area code overlay.
A split means that the geographic region of the area code is divided in two. One part will keep the same area code, while the other section must switch to a new area code (but they will retain their seven-digit number). There is a transition period for this, called permissive dialing, in which either the old or new area code can be dialed for the effected section. After a time, mandatory dialing goes into effect. Then, any call to the new region using the old area code will not go through. These numbers eventually become available for reuse. Splits are not popular with most businesses, as it requires printing new stationary and other changes, as well as reprogramming phone systems. (To avoid repeating this process in a few years, sometimes a three-way split is made at the same time.
An overlay means that a new area code is assigned to the same geographic region as the existing code(s), which is in jeopardy of depletion. With an overlay, no one needs to change area codes. However, if it is not already implemented, ten-digit dialing becomes required for all calls, even local numbers. All new number assignments are in the new area code. As such, ordering a second line could result in a number with a different area code. Overlays are not popular with most consumers, as they do not want to dial ten digits on every call, nor remember different area codes for friends and neighbors.
The area code listings shows all current area codes in North America. If you are in an areas whose code will undergo changes, you can expect your local phone company to provide ample notification in the form of letters or bill inserts, giving you time to make the needed plans and adjustments. However, do not expect to be notified of changes outside your area code. You may bookmark these lists for your call center agents to use as a handy reference, as well for your technical staff in programming area codes in your call center switch.
[From Connection Magazine – December 2002]