Let's imagine the system engineers are smarter than that: if you have a smart phone, you can use the app. If you don't, there'd be a terminal in the station you could use. I'd imagine the engineers for this could have thought of that.
Easy enough to just assume people have smart phones and only have it in cities where mostly people will have them even the poorer people. A cheap smart phone isn't that expensive any more.
It's not just the cost, really: I know I can have a second hand smartphone for peanuts. There'll probably always be some people who don't use smartphones, for whatevre reason.
