I suppose the problem with this is how to pay for the infrastructure like cell towers. I suppose there would need to be ICOs to buy hardware (either existing or new) then the decentralized phone coin would charge nodes (phones) to make transactions (calls, texts) on the chain.
It seems feasible but crypto needs to fet a bit bigger first to be able to take on such a huge project. You would need proper governance to ensure things like maintenance was properly carries put on hardware.