On: Jack White bans phones at gigs for “100% human experience”

[DrScump]

Jamming, yes.

If your venue just happens to block all signals as an effect of its design (working like a Faraday cage), it could legally have repeaters that are powered off during the performance proper.

[tinus_hn → DrScump]

That requires the largest hole in the cage to be smaller than the signal wavelength, which makes it pretty difficult to get in.