Wow, this is some crazy. If you start by assuming they have access to the cell carrier data (which is a super-mega-wacky assumption), why do they need you to p

Wow, this is some crazy. If you start by assuming they have access to the cell carrier data (which is a super-mega-wacky assumption), why do they need you to provide your number in the first place? They can just look it up in the billing, which ties to a verified address. And even if you really are this paranoid, you can just use a $10 burner phone for this authentication.