Comment by peanut-walrus

If SMS actually worked for this purpose, it would be acceptable. However, SMS provides no guarantees about: 1) If it actually gets delivered 2) If it is delivered to the intended recipient 3) 1 and 2 without anyone reading or tampering the message while in transit

Now, even if stars align, your SMS ends up on a route where nobody is mitm-ing or hijacking it, the telco systems work and it gets delivered, it is STILL not a guarantee of identity. It simply verifies that you have somehow got access to a particular phone number.