> Doesn't Google Voice solve this problem? Or perhaps there are restrictions I don't know about.

Only sort of. I wouldn't be surprised if Facebook rejects Google Voices numbers and will only accept a real-live carrier numbers. It seems pretty easy to do, given how often my GV is rejected by sleezy services I'd like to give a throwaway (e.g. peoplesearch opt-outs).

However, I'm not going to personally test this theory by attempting to give a panopticon like Facebook even my semi-throwaway GV number.