All the rest of it is BS. Since they weren't armed I doubt there's any real crime here that can be made to stick.
BTW, if they've installed an improved PBX and done all the correct security procedures for it, there's no way it can be tapped anyway. You'd need to access it over the wire ~ hitting the blocks won't do anything for you.
One of the reasons for certain provisions in The Patriot Act was so the FBI could tap cellphones AND modern PBX mediated systems using modern systems. You can't wait until the call is initiated to start your tap with the good stuff out there today. You have to be hooked up long before a call is made!
Several things, first you don't have to be "armed" to be guilty of interfering or tampering with government equipment. Second, to be guilty of a crime - especially an attempted crime - the state doesn't have to prove that you would have been successful had you not been caught. Your competency as a criminal is completely irrelevant with respect to you actually attempting to commit a crime.
And lastly, it is a federal crime to attempt to gain unauthorized access to secured areas. That, in and of itself is a crime.