One of the surprisingly confusing things when I first arrived in San Francisco was the area codes for phone numbers.

In Korea, you just use your mobile phone number, so I never thought much about it, but in the U.S., just looking at the first digits of a phone number gives you a sense of where the person lives.

At first, I saw a lot of 415 numbers, but then one day I started noticing 628 numbers more frequently. I wondered, "Is this a number from a different city?" but it turned out both are used in San Francisco.

You can think of 415 as the original area code representing San Francisco. Since it has been in use since the U.S. phone numbering system was established in 1947, people who have lived here for a long time still have a strong attachment to 415. I've actually heard locals say, "415 is the real San Francisco number" a few times. It feels like a symbol of an old neighborhood.

However, as the population of San Francisco grew and mobile phones became more common, along with the introduction of business and internet phone lines, it seems that the 415 numbers were almost all used up. So, the new area code introduced in 2015 is 628.

Interestingly, 628 is not from a different city. It is used in the same areas as 415, specifically in San Francisco and parts of Marin County. In simple terms, it's the same neighborhood, but now there's just one more area code. So these days, when new numbers are assigned, many people end up getting a 628.

At first, I thought, "Is 628 for Oakland?" but that was not the case at all. It was just a new number created because there weren't enough 415 numbers available.

In the past, you could dial just the last 7 digits for calls within the same area code, but now you must include the area code, dialing all 10 digits. I remember when I first called a hospital, I instinctively dialed just the number and couldn't connect, thinking, "Is the phone broken?" and I spent a while trying to figure it out.

It turns out this isn't just a San Francisco thing. Looking at the entire Bay Area, different regions have slightly different area codes. Silicon Valley often uses 408 or 669, Oakland and Berkeley use 510, San Mateo uses 650, and Napa and Sonoma frequently use 707. Even though it's all part of the Bay Area, many people can get a rough idea of which neighborhood it is just by looking at the area code.

These days, thanks to smartphones, we hardly need to memorize phone numbers, as we just tap on saved names. However, when it comes time to create a new number or start a business, the moment arrives when you have to choose an area code.

Especially for those running a business or small shop in San Francisco, many still prefer the 415 number. Being an older area code, it feels more familiar to local residents and gives the impression of being a long-established business in San Francisco. Of course, since 628 is also the same area code, there is no functional difference.

Looking at this, I find the U.S. quite interesting. In Korea, we rarely assign special meanings to the first digits of phone numbers, but here, even a single area code seems to carry the history and vibe of the city. Now, when I see a 415 number, I naturally think, "Ah, that's San Francisco," and when I see a 628 number, I comfortably accept it as "the same neighborhood number." What I initially thought were just two insignificant digits have, before I knew it, become a small part of my daily life in San Francisco.