It makes me cringe when I try to call one of my clients about their web marketing and I get a busy signal. When a potential patient or client is trying to contact you about using your services, a busy signal doesn't tell them, "Try back in a few minutes." It tells them, "Call someone else. We're too busy to serve you."
Please, please make the investment in having two or three lines attached to your main phone number. It's a waste of marketing dollars to work so hard to get people to contact you and then turn them away with that annoying BEEP...BEEP...BEEP.
The same applies to letting an answering machine or answering service take all of your calls with the plan on returning the call. There's no replacement for a live person that knows your practice, that can answer the phone, answer questions, and schedule appointments.