You don't have "freedom of speech" when somebody is paying you to talk.

The radio station would be totally within their rights to fire him.

As for his right to say things like that? Sure, I support that right, even when people say horrible things.

But again, as a paid employee of a radio station, you don't have full freedom of speech. You could not, for example, invoke freedom of speech if you got fired for going on the air and saying, "my bosses are all stupid assholes, and they don't pay me enough."

Well, pretty much the same concept here, if this guy did indeed get fired.