To a sizable carrier, a few thousand phones represents a tiny fraction of their subscribers. So a model needs only niche appeal to be of interest.
So AT&T (for example) says to LG: “A solar-powered phone, eh? Could be interesting. Tell you what: we’ll advertise them and you agree to provide the first couple thousand at a decent price, billing us only for those we sell. If they get a good reputation, we’ll convert this into a significant order.”