In the HAM Radio world we use them. But we also use our own infrastructure. I have mine set to let me know when something happens that needs my attention asap. Only works around my stuff or other HAMs that have stuff tied into our system. So not useful outside narrow circumstances.
Depends on the state. Most states from my understanding work like this:
Threatening to throw a rock and/or actually throwing it is assault. When / If the rock hits them then that’s battery.
So in this case the threat of violence is the assault. Had he actually made contact then it would have been battery too.