I used to have memorized a list of major city area codes. It was easy because they were all clumped with similar numbers
| 212-NYC | 312 Chicago | 412 Pgh | 512-Austin |
| 213-LA | 313 Detroit | 413 W.Mass | |
| 214-Dallas | 314 St.L. | ||
| 215-Phila |
Coming across a page in wikipedia… I now understand why the big cities were all clumped.
The Area Code system started back in the days of Rotary Dial.
Instead of pressing a button to create a combination of two notes to identify a number, you turned a dial which would click the line for a count equal to the number. Thus “212” sounded like:
“Fwip-click-click, fwip-click, fwip-click-click”
As a result, the original area codes were passed out to cities based on population to minimize the amount of clicks you had to dial to get thru the the city.
So by clicks:
| 5 | 6 | 7 | 8 |
|---|---|---|---|
| 212 NYC | 213 LA | 214 Dallas | 215 Phila |
| 312 Chicago | 313 Detroit | 314 St. L. | |
| 412 Pgh. | 413 W. Mass | ||
| 512 Austin |
In the initial plan, 605 (SD), 704 (NC), 803(SC) were the original losers with 21 clicks to dial (0 was 10 clicks).
With the advent of tone dialing, the reason an area code is assigned now is to reduce confusion among customers. This is why you get areas with 206, 425, and 360.
So nifty technology history.