Is there any rhyme or reason to telephone numbers? Are area codes holdovers from the days of telephone operators?
The area codes, I understand they're related to geographical locations. There's a little bit of similarity between the next 3 digits of the phone numbers, but I can't see a pattern. Is there any reason they are what they are?
Answers ( 1 )
I worked for AT&T when the network was still "circuit-switched" and not "packet-switched" like it is now. With circuit switching, the network set up a dedicated, direct route between the caller and receiver. Packet switching uses the same method as web browsing does - each packet of data can take a separate route from its source to its destination.
In the old days, the phone network had to know if you were dialing locally or long distance. Area codes always had a "0" or a "1" as the second digit, so if the network saw that, it assumed you were dialing long distance (and then it expected another 8 digits). If the second digit was NOT a 0 or 1, it accepted the next 5 digits (ignoring any additional ones).
In the case of a long-distance call, the local exchange (the switching machine your phone connected to) would pass the call over to the nearest long distance switch. (In the early 1980's, just over 100 long distances switches handled the entire US; of course each switch was the size of a small building.)
In the case of local calls, the local exchange would simply route the call over its own network.
After the area code, the next three digits were referred to as the "prefix" or "exchange". There were some rules (in addition to "the second digit cannot be a 0 or 1") but they could vary from one local region to another. Special numbers like "411" and "911" not only had to take precident, but caused prefixes to not be anything similar (you wouldn't want an exchange that looked like "912" for example because a misdial could go to 911 in error.)
Some prefixes filled up quickly in some places (remember that you can have at most 9,999 numbers in each exchange) if it seemed easier to remember or helped spell a work when letters were added to phone dials.
I haven't checked, but I'd bet that Wikipedia has a lot of good historical information on the old Bell System. It was fun to work there and interesting (scary?) to know that there wasn’t a single person who understood how the entire network worked. Some people knew a lot, but nobody understood the whole thing!