I agree that an extra line is cheap and there are several reasons not to mix business and personal lines. I can tell you from personal experience how, several times over the years I have had to change my personal number because it was the only way to get rid of persistant telemarketers and other people I didn't want calling. You never want to change a business number though unless you want to redo all your business cards, flyers, etc and lose customers. On the other hand say your business does poorly and you go out of business. Do you want creditors and customers calling you at all hours on your personal line? Just disconnect the business line and they won't be bothering you. I've had cheap customers put several businesses under one line then ask me how they can know how to answer the calls with the proper company names. DUHHH!
I don't even leave a message. it's just the default computer voice saying leave a message at the tone.
Very unprofessional. At least record a greeting that says "This is John Smith. I can't take your call right now so please leave a message and your phone number and I will return your call as soon as possible."