The tricorder from Star Trek is well-established as the formative concept for the modern day cell phone. And the idea of a pocket-computer goes all the way back to the calculators developed by TI, designed explicitly against the size of the CEO's shirt pocket to guarantee it would fit.

Miniaturization has been a long time coming. It goes back to clockmakers and glass cutters, trying to turn large scale instruments into portable devices. I don't think it is outrageous to suggest a pocket computer was in the future back in the 1960s/70s.

I do think the speed at which we got here caught people off-guard. But it also set this fantastic expectation for what we'll do next, such that people speculate on faster-than-light travel and AI holograms and robot battle suits and immortality drugs more freely when they can point to "pocket computer" as an already realized possibility.