In many populated cities, talking on the subway/train/etc is considered extremely rude. It changes from culture to culture, but I think it'd be weird if they d

In many populated cities, talking on the subway/train/etc is considered extremely rude. It changes from culture to culture, but I think it'd be weird if they didn't do something with their time since being talkative or social isn't an option. Instead of carrying around a book or sudoku puzzle everywhere for such situations, people just use their phone.