It can’t, but I’m sure that wouldn’t stop Spotify from raising a stink if they see it being bulk imported. I’d imagine this would be similar to OpenStreetMaps and Google Maps; they probably could scrape and bulk import missing info, but they restrict it to licensed sources and user edits to limit liability and enforce quality.

I’m using Ting right now. Cheapest plan is $10 + 5 per gig. I stay on wifi mostly, so that’s fine for me, but there is an unlimited plan for 25. I switched to it because Google Fi had terrible service in my area. However, both services only lease access to the towers, and which towers they connect to has changed over the years, so YMMV.