Call me old-school, but I'm still a phone guy. The primary reason is simple mathematics: if I'm needing an answer to a question, I quickly add up the amount of time and/or complexity that I believe the query will take. If I can knock it out with a quick email, so be it. But more often than not, the time it takes for me to compose, proof, re-compose, take out the stupid joke, re-proof, add the appropriate emoticon, etc., is almost ALWAYS longer than it takes to pick up the phone and make the call.
Of course, the great unknown variable here is "the party to whom I am speaking." One never knows if they'll be available to take a call. And after a day or two of unreturned phone calls, one has to eventually come to the conclusion that they may simply prefer to communicate via email, so then it's time to shift to Plan B (or plan E, if you will).
I've seen this topic discussed across the interwebs over the years and have noticed that those who prefer email often STRONGLY prefer email ("I'd kill before I'd pick up a phone!!!"). If so - why? What's your time worth?