The particular bands the cell providers run in were sold to them by the government (or bought from someone else who got them from the gov). If I remember corre

The particular bands the cell providers run in were sold to them by the government (or bought from someone else who got them from the gov). If I remember correctly it was mostly the antennas lengths and what the tuner was set to for the chipsets (some being fixed, some being more SDR). Some bought those particular bands because they tend to penetrate buildings better than others. But yeah if you could keep inside the power levels, and stay in the unlicensed bands, and keep out of trouble with the patent courts you probably could make an LTE network. I would not be surprised if many of the chipsets already could do it. Power levels would be your biggest hurdle for something more than a test network.