(there is even a rumour that once upon a time phones were stuck to the wall... now that makes absolutely no sense! I am pretty sure that was made up. You would have to go home and stare at the wall to talk to your friends, haha)
With that said, if you ever make an app, I would consider downloading it and trying it out. The map/flag type quizzes would be hard on a small screen, and then the keyboard would take up a lot of screen space too. I currently only use the website on my computers.
Also, where's telegram, signal and other (rumored to be) safer options?