They are the closest thing the city still has to a caste system, defining what is cool, what is dowdy and what is plain whacked out.
Say 213 - the code for downtown and South Central Los Angeles - and people will instantly think of functional public administration buildings, gangsta rap and race riots.
A 626 conjures up the old money and rolling lawns of Pasadena; 323 the hip young scene on Melrose and Sunset Strip in Hollywood; 714 the ultra- conservative dormitory communities of Orange County; 909 the frontierland of the last suburban subdivisions before the high desert.
Area codes are the glue that sticks together the metropolitan mess of Los Angeles. They help to define its snobberies, fears and hidden secrets. All of which helps to explain, perhaps, how the latest changes proposed by the Federal Communications Commission have managed to spark a mini- revolution on the city's affluent west side. The privileged dwellers of 310 land - a mythical kingdom that conjures up images of Malibu beach houses, monster mansions in the Santa Monica foothills, and movie-star palaces in Bel Air and Beverly Hills - are not just angry, they are apoplectic with fury.
The reason? As of a few weeks ago, 310 became the first area code in Los Angeles that needs to be dialled at all times, even for local calls. So all those manicured Beverly Hills hands that until recently had to punch just seven digits to talk to their friends down the street now have to punch eleven of them (the 310 plus an extra 1 for good measure at the beginning).
Not only that, but as of July the 310 code will be "overlaid" with an entirely new three-digit code (424) that will be handed out to new subscribers in the area. Such changes may sound less than earth-shattering, but to westsiders who have worked hard for their prized area-code status, it is equivalent to telling the Queen that Buckingham Palace is now in London SE17, or decreeing that W11 will henceforth be shared between Notting Hill and Peckham Rye.
"You have to understand," the estate manager of a westside multi-millionaire said in response to the change, "the woman I work for has homes in Beverly Hills and Malibu and we're on the phone constantly. The Malibu estate alone has seven-and-a-half acres, a 20,000-sq ft main house, a guest house; there are probably 60 phones on that property alone."
Help is at hand in the form of a $60 (pounds 38) gizmo developed by a westside electronics whizz called Jamie Lieberman, which will automatically dial the 1-310 prefix on local calls. Mr Lieberman hasn't made too much effort to publicise his invention, but since the changeover his own phone has been ringing off the hook.
Councillors and congressmen have had an earful, too, largely from influential constituents threatening to take their campaign contributions or votes elsewhere. Some have hinted at a conspiracy, claiming the Federal Communications Commission has been inefficient in allocating numbers and that the only reason new codes have to be introduced is to make life easy on the private telephone companies cashing in on the Internet/cellphone bonanza.
But it is impossible to avoid the impression that the indignation is fuelled far more by area-code territoriality than by concerns about the inefficiencies of telecommunications number allocation.
New York has had a smack of the same controversy, as the authorities have threatened to infest Manhattan with a rival to its fabled 212 code. But in Los Angeles the debate is made more acute by the fact that the very identity of this notoriously amorphous city is at stake.
The joke, as it turns out, is that the sense of identity is more wishful thinking than hard reality. The current 310 area code might encompass the richest neighbourhoods in the city, but it also includes El Segundo, a cluster of industrial smokestacks next to the airport, Torrance, a depressed suburb full of closed arms factories, and Compton, byword for violent gang culture.
Now if the 424 overlay code could be applied just to that stinking mass, leaving 310 land intact ... You'd never hear anybody air that particular proposal, of course, but it's what they are all secretly thinking.