In big events, most of the time internet connectivity is down. It’s a very fragile system, susceptible to many issues.
Look at in the hard hit Texas gulf area. I’m pretty confident many of those folks down there still don’t have connectivity or they’ve just recently come back up.
The carriers are throwing open all the wi-fi hot spots, so there’s that. And Zello works on cell data.
The Cajun Navy used Zello to dispatch and stay connected in Houston.
I have no idea how they are doing it but my brother is in Rockport, TX where Harvey made landfall and he has cell service, I talked to him the day after Harvey went through.