Why "old-fashioned"?
You are comparing two different things though. "Smart" refers to what the telephone can do. "Flip" means it can be folded closed. I think one manufacturer has managed to create an instrument that is both - the difficulty was making a tightly but reliably flexible screen.
It's only a matter of style. My phone is of "flip" design, light-weight and when folded, is compact enough for even a fairly small pocket; and it is only about seven years old.
I think such instruments are still made, as I hope because the 3D services will end sometime this year so I will need replace it.
As it cost about £45, from memory, I suppose I will have had my money's worth from it at just over £6 per annum write-down! (My PAYG call costs are well under £50/year.)