This might be of interest not only for a burner number but also as a cheap and secure mobile line to use as dedicated 2-FA where SMS is the required, and only, available method.
Ting (ting.com) offers mobile service for $6/mo/line. They sell SIM cards for $1 so buy a few, then you can always spin up a new line on-demand. They support TOTP/U2F 2-FA, toggling call/text/data service, block porting, multiple call forward options, device auth/deauth/activation/suspention, # port blocking, etc., competent friendly humans provide on-demand phone support, and unlimited hassle free referral bonuses (you get $50 for initial referral $25 for unlimited others, people you refer get $25).
