The Development of the Area Code

The Atlantic looks at how phone area codes became an identifier of who we are and where we are from.  I found the way AT&T engineers came up with the original area code system to be pretty interesting:

Engineers at Bell Labs designed the numbering scheme beginning in the early 1940s and working into the next decade. They took advantage, in that, of a supremely rare and an even more supremely geeky opportunity: to design a system, from scratch, that would ensure a maximum amount of efficiency for a maximum number of phone users. The area codes that lead our own phone numbers today—212, 202, 415—were direct results of their work.
They were also based on a particular type of hardware: rotary phones. To use those phones, you placed a finger in the hole of the number you intended to dial, then rotated the dial clockwise until you hit the phone's finger stop. What this translated to, as far as the phone was concerned, was a series of clicks. Lower numbers on the phone, starting with 1, registered a lower number of clicks than the higher ones. What this translated to for the human user was less time required for dialing.
The system Bell's engineers devised married the hardware of the rotary phone to the machines that would provide the infrastructure for the nation's expanding phone network. Computers, back then, were primitive. To ensure that area codes would be recognizable to the computers that were to translate the codes into geographical areas, the engineers created a system that placed either a 1 or a 0 as the second digit in each area code. (Those with 0 in the middle indicated states with only one area code—hence DC’s 202 and Florida’s 305—while those with a 1 denoted states with multiple codes.) The system meant that those early computers would be able to distinguish between a long-distance area code and a local number. Which meant in turn that they could route calls across the nation, to regions of the network and finally to local networks.

When it came to creating the area codes for the country, the engineers also made their plans with maximum efficiencies in mind. New York, the most densely populated area of the nation, got 212—2-1-2 containing the lowest number of clicks possible on the rotary phone. Los Angeles got 213—the second-lowest—while Chicago got 312, and Detroit got 313. Anchorage, Alaska, on the other hand, got 907, which required 26 clicks from the person doing the dialing. To make the system even more efficient and human-confusion-proof, engineers also ensured that codes resembling each other (say, Oregon's 503 and Florida's 305) were distributed far apart from each other on the map.
The whole scheme “illustrates how smart the Bell engineers were back then,” Phil Lapsley points out. They were trying to design a system that was user-friendly—with the user, in this case, being the nation as a whole. They were also trying to design a system that would be, as much as possible, future-proof. There were, given the possible permutations of the rotary dial, 152 potential area codes. At first, only 86 of these were assigned. The engineers, in outfitting their new network, had given it room to grow.

It is pretty cool that all that went into it, and they worked out all those details.  That system has grown pretty well since then.  It amazes me that Florida only had one area code back then.  How times change.