Here's a piece of folding hand-held tech, extremely thin, NO mechanical hinges! And I don't think Casio have made calculators like this for 20 years or more now.
Must be 20 years old at least, it's "Made in Japan", not China. Probably had very light use.
From experience they never lasted too long, especially when given typical school or college use. The keys on the right side often wouldn't work because the flexible conductors, probably flexible printed circuit, have failed with stress fractures, because of repeated bending at a small radius, i.e. fatigue.
So I'm thinking if they want to make a thin foldable phone
without hinges, they got to find plastics, metals and a display that can withstand
repeated bending thousands of times, at a narrow radius and doesn't fail or break with fatigue. If there's hinges and a definite split in the device where it folds, you've basically got the Kyocera Echo again!!....LOL