If a builder picked up the phone anytime it rang, he'd never get anything done. Call, leave a message, wait. If you wait more than a week, call again. That being said, Cam at Redline has always spent time on the phone with me anytime I got him to answer and was more than willing to answer any question that I had.
He also finished my engine right on time and far exceeded my expectations with performance, support, and pricing.