Ultimately, it's the government that mediates the dispute. They're the government's airwaves and you (the cell phone provider) receive a license to use them. I haven't read the relevant FCC regulations, but they can easily say "cell phone service is secondary; law enforcement is primary".
There is precedent: amateur radio operators can use any means available to them to transmit life-critical messages when licensed methods/frequencies don't work. If that was to set up a fake cell phone tower and get phones to connect, then one could argue that one was using the frequencies legally. (IANAL; don't do this and say I said it was OK. The usual case is something like using your amateur radio to contact the coast guard if your ship is sinking.)
There is precedent: amateur radio operators can use any means available to them to transmit life-critical messages when licensed methods/frequencies don't work. If that was to set up a fake cell phone tower and get phones to connect, then one could argue that one was using the frequencies legally. (IANAL; don't do this and say I said it was OK. The usual case is something like using your amateur radio to contact the coast guard if your ship is sinking.)