The defendant and his girlfriend were arguing, and the defendant punched the girlfriend. Neighbors saw the punch and called the police. As they were arriving, the defendant left in his car. While the police were talking to the woman, the defendant called her on her telephone. The police officer held the phone and heard the defendant say" If you get a wrrant on me bitch I will kill you" The defendant was arrested and charged with making a terrrist threat.
This is another example of how things have changed since the Patriot Act. If someone is charged with making a terrorist threat, it is often a he said, she said situation. In that case it depends on how believable the witness is and whether or not the witness recants. In this case, however, the police officer heard the threat. I would think that if she handed him the phone or the phone was on speaker and everyone heard, the conviction should be fairly easy compared to most of these cases.
I am not sure that the expectation of privacy extends to threatening another person's life; and even so, one would assume that the girlfriend could relate the conversation to the policemen. Under the res gestae exception to the hearsay rule, it is doubtful that a court would find the statement inadmissable. A bigger issue from my perspective is charging the boyfriend with terrorism. This appears to be more of a domestic situation in which a particular person was targeted, not generalized soft targets that constitute terrorist attacks. The threat was "I will kill you," not "I will blow up the subway station." A charge of threatening the life of another; or criminal domestic violence would more likely be sustained. "Terrorist threat" is a bit much.
There is only one problem I can see that might prevent a conviction from being obtained. This will depend on the way in which the officer came to be holding the phone.
As you can see from the "threats" link below, the boyfriend is clearly going to be factually guilty of making a threat. As the link says, all states have laws against threatening to injure another person. In this case, the boyfriend has clearly threatened to harm the girlfriend.
However, if the girlfriend ends up siding with the boyfriend (as sometimes happens with abused women) there may be a way to claim that the conversation was overheard illegally. Let's say the girlfriend answered the phone and told the police it was the boyfriend and the officer took the phone without asking permission. This might be construed as illegally listening in on a private conversation.