Before I get into the meat of the second (and last) of these weekly checks of the prosaic, I did want to note how different area codes are from just about every other categorizing motif. In systems such as the Dewey Decimal or Library of Congress library catalog systems or the North American Industrial Classification System (NAICS) for businesses or last week's adventure, ZIP Codes, like things tend to be close to each other numerically (or in the case of the LC, alphanumerically).
However, most area codes are intentionally diffused so that the user isn't confused by a similar number in the same area. So, in upstate New York, for instance, 315 (Syracuse/Utica area) is adjacent to 585, 607 and 518.
When I was a kid, I could tell you just what a legitimate area code looked like. The first digit was 2 to 9 (but not 1), and the next two digits were either 01 to 09 or 12 to 19. This is a now-useless skill comparable to being able to figure out square root with pencil and paper (which I can, but not as quickly as one can just type in the number and a function key on a calculator).
These numbers were so allocated this way because of some sort of design limitation. However, when it became apparent that they would soon run out of phone numbers, because of increased use of cell phones plus blocks of numbers being sought by businesses, technological innovations made it possible to greatly expand the pool of area codes.
All of these machinations are controlled by NANPA: the North American Numbering Plan Administration. "This site provides information about the North American Numbering Plan (NANP) and its administration. The NANP is the numbering plan for the Public Switched Telephone Network for Canada, the US and its territories, and the Caribbean."
I remember back in 1984 when New York City was split into two area codes, 212, the code since at least 1952, and 718. Manhattan got to keep 212, but the outer boroughs, Bronx, Brooklyn, Queens and Staten Island were burdened with 718, deemed as an "ugly" number by a NYC tabloid. Likewise, my old college town of New Paltz used to be in 914, along with the rest of the Mid-Hudson valley. Westchester County got to keep 914, but the rest of the area was switched to 845 in 2000. This list is now out of date, but shows the early changes.
As this source explains:
"Split" refers to a service area served by one area code being subdivided into two or more areas, with the original area code serving one of the subdivisions and new areacode(s) serving the other(s).
"Overlay" refers to a service area being served by two or more area codes simultaneously. usually i write "X overlaid on Y" to mean that X is a new areacode that will service an area that previously was serviced solely by Y.
The advantage of a split is that for intra-service area dialing, only 7 digits are required, but some existing users will be forced to change their web site, stationery, business cards, etc. In contrast, an overlay only affects new customers, so is less of a burden; however, neighbors may have to dial 11 digits to call each other.
It appears that the small hassle of dialing 11 digits, even within the same area code is far less burdensome than whole areas having to let friends and associates that they have a "new" number, as most of the recent changes seem to favor the overlay - my mom's 704 overlaid with 980, or 917 overlaying all of New York City, ostensibly for cell phone service, but not so limited at this point.
There are still some area codes that will not be used, and it includes those ending in 11. That's because the three digit numbers are otherwise allocated.
N11 CODE DESCRIPTION
211 Community Information and Referral Services
311 Non-Emergency Police and Other Governmental Services
411 Local Directory Assistance
511 Traffic and Transportation Information (US); Provision of Weather and Traveller Information Services (Canada)
611 Repair Service
711 Telecommunications Relay Service (TRS)
811 Access to One Call Services to Protect Pipeline and Utilities from Excavation Damage (US); Non-Urgent Health Teletriage Services (Canada)
The Albany, NY area just got a 211 service in April 2009.
There are also a batch of area codes that are toll-free, though they may be limited by geography. 800 was the first, followed by 888, 877, and 866, with 855, 844, 833 and 822 held in abeyance.
T is for transportation: bus, bike
23 hours ago