From what you said, you didn't make any threats. You should not speak to the detective yet, until you have legal representation. You can get a count-appointed lawyer or defense attorney right? Why not just let them do their job, and don't stress it. You should document your own phone call to prove that you made no terrorist threats- you need to subpoena with a lawyer or request your own phone records. This is a serious allegation, that is definitely no joke. I can relate to exaggerated allegations that were later proven false, I would not panic. Just stay out of trouble and don't speak to detectives without the presence or advice of legal counsel. You can also possibly file a complaint. That is why you really need a lawyer. If they start harassing you or seeking conviction, that would be very bad to be put away for terrorism for making a prank call.