I've got a small local ISP by me that runs fiber to the home in rural areas and wifi as well. Them for a start. I would imagine Google and Elon musk if the price were right.
In one of the previous auctions they tried and failed to outbid Verizon and that was "only" $4.5 Billion or so. Imagine if Google Fi were based on a single country-wide chunk of spectrum exclusive to Google instead of them being an MVNO. Verizon did and made sure Google lost! If Google fiber is any indication, cell phone companies would have faced very stiff competition.
