I think he's saying that the act of detonating a bomb, or attempting to detonate one, is illegal all by itself. The fact that it was done by a phone call doesn't change anything, so, the phone call itself was not illegal. The charges would be identical if they used a phone or a timer or a hand switch.
That's why I brought up the example of wire fraud, which is basically any fraud committed using electronic communications. This charge is usually added on top of the main fraud felonies despite the fact that the only difference is the medium of communication. In the case of wire fraud, a phone call does change the crime in the eyes of the court.
