Why no smartphones in DBZ

Like Vegeta said, you'd think a civilisation as advanced as Earth would have a smaller clock. Well, they did have smaller clocks.
Likewise, where are the smartphones? You'd think a civilisation with flying cars, capsules and time machines would have smartphones already.

Not much of a topic, just a random thought I had when looking at that Namek chapter the other day.

Bulma was able to communicate to earth instantly from across the universe yet they don't have smartphones

There are smartphones in DBS. The reason there weren't any before is because smartphones weren't a thing back in the 80s or 90s.

Piccolo uses one in Super Hero.

Maybe communication was advanced enough to where they didn’t need smartphones.

You can have a certain level of technology but people may not get inspired to combine technologies in a way to make a smartphone. Meso-Americans could build advanced pyramids but didn't even have the wheel.

The real answer is the writers add technology that is present in the real world at the time of writing. In-universe you could say smartphones weren't invented until post-Buu saga.