re:but I'm still curious about this pattern for area codes that I perceived back in the 70s. Any rationale anyone knows of for this?
2 reasons
First--because 0 and 1 didn't have letters assigned to the numbers, there were virtually no exchanges that used these numbers, so it was an easier to set up.
second--once you lift the reciever, the voltage on your phone increases from 5 volts to 40 volts, and you are not charged for this higher voltage until you connect. (the cost of the call is partly the energy cost)
so areas with high volumes (large cities) got numbers that could connect faster with the old rotary dials. NY's 212 is the fastest code to dial, 909 is the slowest.
business numbers with zeros--555-1000 were charge a premium for their all zero number, too.
now that 95% of US is wired for digital (touch tones) all area codes are equal. it doesn't take any longer to call 909 than 212.
when the 1+ area code came in, it allowed for area codes with out 1 or 0 in the middle, and for exchanges with 1 or 0 in the middle
this really increased the number of area codes, and the number of exchanges available, with out resorting to 8 digits for a basic number. so everyone thinks of there telephone number as 7 digits (US!) plus 3 for an area code, and first dial one. (really 11 numbers!)
the good news is we missed out on all the fun that our friends in UK have had, where the origanal plan was didn't offer enough numbers, and then with cell phones, the need grew again, and they ran out of numbers again!
