If you think about it, if the attacker is sophisticated enough to break the phone within a 72 hour window, then they are definitely sophisticated enough to use

If you think about it, if the attacker is sophisticated enough to break the phone within a 72 hour window, then they are definitely sophisticated enough to use a faraday container. So communication between phones wouldn't help very much. Moreover, you'd have to have some inhibitory signal to prevent everybody's phones restarting in a crowded environment, but any such signal could be spoofed.