I've wondered about the right answer to advertising for 20 years. In the beginning I felt it was needed to build a customer base. I always seemed to feel bad about it though. When I was very busy, I didn't have time to handle the calls. When it was very slow, I didn't have money for the bill. I especially felt that these slow and busy times were unrelated to my advertising.
I tried a phone answering service, but was always training the people. There's also something in the forwarding that can leave you without a ring for a long period (double the space between rings). I have a basic deep dislike for yelling at people with a bad cell phone, and I don't like to stop working to take sales calls.
In the end I don't advertise and rely on repeat business and referrals. I've tried direct mail with miserable results (I think 2% is considered good). IMO networking works the best. I'm a member of a large church, which is maybe 10% of my business. I probably get another 10% in non-church referrals, and the other 80% is repeat business.