The carrier is Phreeli https://www.phreeli.com/about-us and it's from the guy behind https://www.calyxinstitute.org/. I used a Calyxinstitute wifi hotspot for a few years and it was a mostly good experience. The only bad thing was cell carrier support for my hotspot got dropped and I was SOL. I don't blame them because it's kind of expected with that kind of barebones service that gives you what you need and nothing extra. I probably could have avoided it if I did more research and picked a different device. Oh well.

Phreeli has a $35/mo plan with unlimited data. If I decide to become a smartphone user again, it seems like a good deal.