That is because many Fujianese restaurant workers are not educated and thus don’t really read and write English. Given that. How do you divide the United States? Not through towns and states. You do it through numbers — hence the area codes. As I wrote in a piece in 2005, job listings in Chinatown employment agencies are often done by area code.Here's a snippet from that earlier article, which is well worth reading.
For workers who cannot read the names of their destinations in English, area codes serve as the restaurants' main geographical identifiers. The workers do not see America as a series of cities or even states, but as a collection of area codes, almost all with dozens upon dozens of Chinese restaurants looking for help. Maps in every Chinese agency break down the country by area code, with recently introduced area codes scribbled in by hand.via Culture-making
For many restaurant workers, the number of hours by bus is a critical measure of how far they are from the American center of their universe, East Broadway in Chinatown. Almost all travel by bus, because many do not speak English or have identification, so they cannot travel by plane. A network of Chinese bus companies has sprung up to shuttle the restaurant workers from Chinatown to the rest of the country. Some have started to draw non-Chinese riders, specifically the "Chinatown buses" that run between New York and Boston or Washington. One bus-company sign advertises the destination and the fare: "Minnesota (612, 551, 952, 763) $150; Wisconsin (920, 715, 608, 414) $120."