I don't think the assumption that SMS is enough is valid anymore.

My wife's elderly aunt has a flip phone that can receive SMS but not MMS. We just went thru an "identity verification" procedure with a major bank last week that sends MMS, not SMS, and could not reach her flip phone.

The whole ordeal was a huge pain in the ass and if my wife and I weren't there to help her it would have been completely impenetrable to her.

I could also buy a smartphone. The point is that I shouldn't have to.

Sometimes the code must be received through the bank’s app. I went though this process recently to open a new account (at a bank where I already had other accounts). I didn’t think much of it at the time, but if you didn’t have or want a smartphone, this could be a major problem.