I have seen some "projects" using the power of smartphone. But guess what? Almost 99.99% of those projects are scam! They use your smartphones computational power to either do something else, or they just collect data, sells them and shares a minuscle portion of the profit they make with you. Not worth the power you will be spending. Again, smartphones aren't "cabale" or built to be used for heavy computational purpose 24/7.
There are so many possibilities therefore. Right now I had the idea of creating a decentralised internet (or messenger at least) based on Bluetooth (or wifi) p2p Network, so it still works after the regular internet may break down.
Bluetooth and wifi based p2p messaging system already exists. People use those when the government shutdowns internet due to political unrest.
Internet? I doubt that's possible. Risks plus efficiency would be a problem.