Never let a call just go to voicemail.
We've got someone to answer our phones and that is all they do.
The return on having someone just answer the phone to take messages for you, give our hours, address, basic prices and hang up on telemarketers is worth every penny.
Here is a perfect example of why you answer the phone: About 3 months ago It was about closing time. Phone Rings my receptionist answer it and she couldn't answer the question so she transfers the call to my office. Guy said he left message with my competitor about a sign but he never returned his call. I was able to answer his question about channel lettering. The next morning I've got a check for 4k. Now my competitor we'll just call him Larry, is a one man shop and does his installs after 4pm. So even though this was one of Larry's past customers and I'm sure Larry would have been able to do the same sign job and been about the same price, I got the job not because I've got a good reputation (which I do) its because picked up the phone and said Olson Signs.
Also on a side note: If you've got people begging you to do sign work its not because you don't answer your phone, its because you are prices are too low and they'll deal with crappy customer service for a good price.