jazz-- you'll be sorry you asked..
Phone numbers are made up from a series of groups.
011 is the internation access code.
then there is the country code.. A two digit number,
then an a two or three digit city code.. In US, known as area code.
An exchange code – directs you to a specific exchange (or switching office) finally, the last 4 digits go your house.
When direct dialing first became available, most phone where analog.. (rotary dial)
a phone, sitting, unused, takes about 5volts to keep it active, but 40 volts to ring, get dial tone, or speak.
So, the minute you pick up the reciever, energy use goes up– big time! And the company doesn't start to collect money, till you connect with your party.. So the telephone companies had an interest in speeding your connection time.
To speed the time from when you picked up the reciever, till when you where connected, cities with high volumes of calls got area codes with "low numbers" , since on a rotary phone, you can dial 212, much faster than 909.
similarly, phone companies, assigned exchanges to business areas, with lower number, or charge extra for numbers with zero's . and smaller communities got higher numbers for exchanges then the surrounding city.
Digital dialing changed the economics, since its just as fast to dial 909 as 212. But the old exchanges still reflect the economic alignment. (And for the first 20 years, of digital phones, the company actually charge you more to use them, even though they saved money when you did, because 1) they dial (and connected) faster, and 2) could be programed for speed dial!)
Then to make things more interesting, in large cities, (NY, Chicago, LA) most phone systems have run out of numbers.
NY's solution was new area codes. For the past 10 years, only Manhattan is 212, the rest of the city is 718. Cell phones, beepers, etc., are 917, and we still have run out of numbers. Manhattan now has a second (and hated!) area code.
but even that was not enough. Now days, all most every phone system in US requires 1+ area code. (Then the number) the 1+ lets them use area coded that do not follow the old standard (the old standard was, all area codes have 1 or 0 in the middle.)
since old exchanges always used letters as a prefix, FOrdham, BEechwood, MUrrey, and 1 and 0 didn't have letters associated with them, these numbers where never used as exchanges..
