Don't cbrs devices need to be part 96 certified? The spectrum might not be licensed but you still may need a certified device to legally use the spectrum. Which you could do, but that is a tall hill to climb for a FOSS enthusiast. And when you're done -- what network are you going to connect it to? A cheap SIM from the corner store is probably out of the question :)
looks like they need.
but it still gives you more possibilities compared to usual spectrum. if there is enough coverage from SAS you (or FSF) can build your own cbrs network that will have open source modem/firmware (yet, still will have to comply with part96).
there are also all kind of open source lte/cbrs projects iirc
It's a fun thought exercise, but putting "part 96 certification" at the end of my build pipeline sounds pretty expensive. And building a physical cell phone network is stupidly capital intensive. Maybe there are some interesting small scale niches that this would be useful for. But as a daily driver cell phone, I don't think we're ever gonna have an open source modem, at least not until there are significant changes to the spectrum that's in use.
