Effective way to deal with misuse of mobile devices in class I'm at a North American, state-run university (not an elite institution), which is relatively modern in terms of supporting mobile devices. The school is proud of its WiFi coverage in every classroom, and recently rooms were updated to have electrical outlets at every student's seat (even in auditoriums), so they can charge their devices. All courses are three-hour periods, once a week.

This mobile-friendly environment is great when integrating mobile technologies in class. I make use of Mentimeter (real-time quizzes), the students can follow the PDF lecture notes and/or electronic copies of texts, take notes on their laptops, look things up on the web when I ask questions or when they do exercises, etc. 

However, it makes for a challenge during courses when students use these devices in distracting ways. Definitions of "misuse" are situational, but for this question, I'll call it any use that detracts from a healthy learning environment. Concrete examples include watching a video or playing a game on a laptop (distracting neighboring students), texting, using Facebook rather than working an exercise in group, etc.

Laptops and smart phones in class are not new; in the past I was able to deal with their "misuse" relatively easily. A student would be easily embarrassed and close his laptop if you called him out when you saw that 5 students around him were all looking at his screen and smiling. I ask a lot of questions during my classes, so I could "pick on" students who caused disruptions with their mobile device (or otherwise). Drawing attention to one student in large groups is an effective way to change behavior, usually.

However, last semester was more difficult than ever, with 40+ students in an newly-electrified auditorium. During one class interruptions occurred 3 times, and I had to talk to offending students during the break about it. During the mid-term, I had one student argue with me at the start because he wanted to keep charging his iPhone at his desk in front of him. He insisted he wasn't going to use it during the exam to cheat, but I cited the policy barring mobile devices during exams and mentioned he'd have to explain that to a discipline committee - he complied. Needless to say, those "correctional" situations don't win points for the professor in the course evaluation. On the other hand, I learned that if I don't intervene (early in my career I would ignore these behaviors), students who feel distracted will complain during evaluations (most are too shy to say something during the semester).

The solution it seems is to add yet another item in my already lengthy syllabus and explain the desired behavior during the first lecture. My school has no official policy as far as I know regarding mobile device use, apart from an IT security policy that doesn't address the distraction issues. I did some searching on the web and found that some schools have policies, e.g. McGill. What is not clear is how effective the policies are in large classrooms, how easy they are to enforce without becoming the "text police", how well they work in non-elite universities, etc. 

I contrast all this with the fact that my students almost never misuse the "phone" part of their devices (they don't ring during lectures and they don't talk on them except at the breaks). None of that is in my course plan and I never have to explain it at the start of the semester or take action. 

So, how to reduce misuse of mobile devices in large classes while maintaining a friendly atmosphere?

EDIT see this article for the students' perspective of the problem, and why it's not like other classic forms of distraction. In the conclusion, they state it could be useful for institutions to define policies about proper behavior in the classroom regarding mobile devices.
There is nothing new in what you describe. As a student who oft got bored during lectures, I have done some distracting things during them, even though I didn't have access to any electronic device at the time (I'm young enough that they existed, but it wasn't accepted practice to bring them to class). We did crossword puzzles (collaboratively), we played cadavre exquis, we read newspapers and discussed them, we flirted, we worked on other stuff, … What makes you think the situation you are experiencing is specific to mobile devices? The cause of the distractions is different from other situations, but I think the issue is the same and the solutions are, too.

So, what I would suggest is: warn your students that while what they do is their business, you expect that their behavior does not interfere with other's study or the general class atmosphere. Tell them that mobile devices are useful, but that they should be careful not to abuse them. Handle non-compliance as you would a typical incident: talk to them, give fair warning, but clearly set the limits and enforce them if it comes to that.