When I lived in Seoul in 2008-2010, people were not only using smartphones, they were watching television on their smartphones, in the subway. Smartphones in Korea have built-in TV tuners.
And yes, the social norm is and has been to ignore the people around you as much as possible, even more so in East Asian cultures, and more so when it's very crowded. If everyone were talking and socializing, it would be very loud in the subway car.
And yes, the social norm is and has been to ignore the people around you as much as possible, even more so in East Asian cultures, and more so when it's very crowded. If everyone were talking and socializing, it would be very loud in the subway car.