Temporary separation of the bonephone from the addict results in growling and snarling.
"As people enter the venue, their phones will be placed in Yondr cases. Once they enter the phone-free zone, the cases will lock. Attendees maintain possession of their phones and are now free to enjoy the experience without distraction... If at any point attendees need to use their phones, they simply step outside of the phone-free zone to unlock the case."
It's a good compromise.
Simple. Easy. Effective.