Email is better....for all parties.
They always get back to me, on email, and I'd hate to take a reamer print over the phone...absurd. Hey if you just wanted the neck and freebore..maybe, but I'd rather read the print myself.
I do not agree with the phone advice, email is more efficient with less chance of communication error. If your pressed for time, a phone call, although interuptive to a vendor, will let them know of your query sooner "Sir, I sent you an email about...."