This is one of the reasons its a fun idea. The TV bands (50 - 210Mhz) can cover a huge area from a single antenna (that was their original modality) but because of the inverse square law, it means that a much smaller and lower power antenna nearby can still get a big chunk of real estate. During some experiments at a company that will remain nameless it was something like 1 antenna could easily cover 2 mile diameter circle, 4 would cover 8 square miles, and 30 - 40 could cover nearly all of the cities around the SF bay.

The actual cellular mechanics are quite an undertaking, but something along the lines of a coded point to point system would be implementable by a small group of people.