Rule #1: Return phone calls. Always. Even if you have no idea who the journalist is, and no intention of talking to them anyway. At least have the courtesy to say so.
I've recently run into a cluster of people who don't seem to have figured that part out. Very frustrating, but it ultimately hurts them more than it hurts me. I can always write about someone else, while there's no way to recapture a lost opportunity once the publication goes to press.