I’m disappointed that LTE Direct didn’t take off. It sounds like it has to be builtin to firmware or even requires hardware changes, and manufacturers didn’t add it. Probably cause couldn’t see way to make money.

It would be perfect for short-range comms, replacing walkie-talkies and messaging. It would work with phones that people already have.

For mid-range, cell towers on hilltops with link to other places would work. Except I heard cell towers need a lot of network infrastructure to work. And may consume too much power to work off solar. Simple solar-powered, self-contained cell sites would be useful for disasters and other events.