Question: "And math and radio may be uniquely human ways of doing things. If we were intelligent crustaceans, would radio be important to us?"

Answer: I believe that certain things in the Universe are constant like math, and yes even radio.

The concept of 1 object added to 1 other object equals two objects is going to be the same for any type of intelligent life no matter what their body looks like, or what they call the two objects together, the concepts the same.

The idea of radio stems from the discovery of magnetism, and then electricity, after that it's just a matter of time before radio waves are detected and produced.

I believe this is true perhaps even on a planet with no permanent magnetic field because I think it is possible even on that kind of planet to have Iron meteorites and lode stone which is magnetized.

Still the inverse square law applies to radio waves, and any thing that moves at or below the speed of light just isn't going to be any good for interstellar comunications.