I have known that SMS is not secure, probably since when I worked a bit with SS7 protocol before. But I do not know it can be "hack" for $16. Joseph Cox wrote for Vice about "A gaping flaw in SMS lets hackers take over phone numbers in minutes by simply paying a company to reroute text messages". The white-hat hacker then took over WhatsApp, Bumble, and Postmates accounts of Cox. All for $16. For long, SMS has not been considered secure, especially for authentication. It is not even personal as an email because you do not really own a phone number, or we should say differently that you are much closer to owning an email address than a phone number.