Question about Pretext Phone Calls

I don't really know how trials work and who is entitled to what so I've always wondered- this the defense side hear the pretext calls before trial? Did they know they were coming or were they listening to them for the first time in court, wanting to hide? Just curious. I would assume that pre the trial both sides get to review a certain amount of evidence before hand, but wasn't sure if the calls would be something the defense side would have access to prior. Any insight would be appreciated!