If some professor wrote a paper or book about a subject or got their work mentioned in the media the odds are pretty good you can look up their phone number in a campus directory, have them answer, and ask a question about the paper and typically get 10-15 min to talk. Generally people like that are happy that people are interested in their work and you often get a good response.
If I have a focused question about their work and have a PMA about it, I would say my success rate is awfully close to 100%, in fact I cannot think of a time where I did not get a thoughtful response.
Anyway, Tim Ferris talks about this in the "4 hour work week" and says pretty much what I told you. It may be intimidating if you are not in the habit, but people who write books and other literature are usually very happy to hear from readers. Getting a whole hour might be tough, but 10-15 min on the phone is not that hard.