Eh, I wouldn't be that surprised if it happens from time to time for big events. You'd be talking the very big sophisticated ones, but it is possible to get temporary licenses, and the equipment isn't _catastrophically_ expensive, particularly if you're just renting it.

This: https://en.wikipedia.org/wiki/Chaos_Communication_Congress usually has a temporary cell network (I think up to LTE last year) set up for the duration of the event, on a temporary license. And that's basically just done for fun.