While the security of centralized messaging is potentially an issue, one thing I don't think we've got a global consensus on tech-wise is point-to-point systems

While the security of centralized messaging is potentially an issue, one thing I don't think we've got a global consensus on tech-wise is point-to-point systems that will work with smartphones and no internet. I know there's a number of approaches out there, but I haven't seen anyone solving the problem of doing offline-relay from device to device with the goal of getting the message out to a wider aggregator without internet access.