BigThings, this is Roger. For many voicemail systems, pressing zero will route the call to an attendant. Even if you don't list this as an option, some voicemail-savvy callers will hit 0. Have something prepared for them, even if you can't spare a live attendant. Two possibilities are a return to a main menu or alternative contact information.
Some companies still do things the old-fashioned way and have a real live person answer each call.
This approach is laudable, but can be taken too far. You have reached BigThings, Incorporated. Normal business hours are 9 to 5, Eastern Standard Time. Please leave your name and message at the tone. Finally, if you are self-employed and use your main home telephone for your business, answer calls in a businesslike manner.