112 seems to be the best phone number if you're dealing with a standard dial phone (rotary). You don't have to wait so long for the dial to spin back before the next number.
The city codes in the USA were implemented so the largest cities would have the smallest numbers: eg. NYC was 212. Los Angeles was 213 and Chicago was 312.
So when you wanted to dial to New York from...say Boston (614), you didn't have to waste so much time dialing the city code before starting in with the number. A city in Utah for instance would have gotten something like 804. Washington D.C. used 202.
Of course, cities have long since outgrown these codes. The venerable 212 is now only used for Manhattan and it has now been "overlaid" with 646...a combination that makes people think you're in Colorado or someplace where all these "new" area codes are sprouting up.
Now you have to dial the entire 10-digit sequence anywhere.
It used to be you would dial seven numbers if you were in the same city code. Now it doesn't matter. If you're in 212 and you want to dial another 212 number you have to dial 1-212-bla blah blah.
If you're in 718 (a New York City code instituted around 1982 for Queens, Brooklyn and Staten Island - now also serving the Bronx) you have to dial 1-212 to get into Manhattan and 1-718 to other numbers in these areas. 1-718 has also been overlaid by another area code.
The +1 indicates it's "long distance" (even if the call is inside the city).
I think the easiest thing should have been a split - with the older part of Manhattan (southern Manhattan) staying with 212 and the northern part becoming 646. But the regulators thought otherwise.
