I guess I can see both sides of this, but I personally prefer the phone or the best option to me which is meeting in person. It seems as though these Facebook messages always go the same way. I have to message back and forth to get as much information as possible for an accurate quote. Over the phone I can pull up a quote sheet with all the necessary questions that need addressed and do a thorough job right off the bat, with no need for the back and forth nonsense. They can get their quote quickly and accurately and I can get on with business and await an answer without all the headache.
Emails, on the other hand, aren't as bad and I can manage them, but I still get a lot of the back and forth conversation before an quote request can even be placed. It's like the generic "How much for a 4' x 8' sign?" question. I have to take the time to figure out what kind of graphic, what kind of substrate, etc., all of which could be easily addressed over the phone.