Continuing with the idea of using cell phones in class for good and not evil, how about a backchannel? Today's Meet is an easy to use (and free!) service that allows users to post to a feed remotely, using desktop or mobile devices. You create a free account, set up a "room," provide the link to your students, and they can add their thoughts, questions, or responses to the feed. There's a nice projector view you can use if you'd like that option, and you again have moderator control (you can even mute specific students without them knowing they're being muted).
You can give it a try right here! Just enter a name (or alias) where it says Nickname, click Join, then type in your thoughts. How about something you're reading this summer?