In what way is this a limitation of free speech not granted within the precedence of free speech rulings? Or better yet, why do you think this is protected under free speech.
This question seems backwards. Any expression is free speech by default unless explicitly ruled otherwise. The burden is on people wanting this ruled out to argue it isn't free speech.
So you feel it should be legal to call in bomb threats to schools? It's free speech after all.
Even a cursory glance at the legal code should convince you that "free speech" is a convenient fantasy mostly used to hoodwink liberals into supporting the KKK. Why not call it a "speech" issue?