There are flaws to their methodology. For half the companies, to change your number from A to B, you first must verify a NONCE with A, then verify a NONCE with B. This just means you have to possess two phone numbers for a period of time — Weeks, or in reality, months — while you change the long list of services over to the new phone number.

There is a simpler/better way and that is to verify you have your email address before allowing you to do a NONCE with B.