How do you deal will the cellphone epidemic?

I thought it would be nice to share approaches. No matter the demographic of students we teach let's face it, we all deal with it.

Edit: I figured i would add my approach. I allow it until it becomes an issue, that issue being they are no longer concerned about anything i have to teach. I've had students be responsible and just use them in the down time we have. I have had students get sucked into an alternate reality you struggle to bring them back from. Unfortunately as it always goes, the latter ruins it for everyone.