I have no idea how well this works, but the Serval Project aims to let people communicate when the network is down: https://en.wikipedia.org/wiki/Serval_Projec

I have no idea how well this works, but the Serval Project aims to let people communicate when the network is down: https://en.wikipedia.org/wiki/Serval_Project https://en.wikipedia.org/wiki/Serval_Project