Expanding on the simple approach above, let the caller know who they've reached. This will not only eliminate people leaving voicemails by mistake, but it will reassure the caller that they have called the number they intended.
Since I pride myself in being responsible, if I don’t receive a return call I have to assume I wrote down wrong number. If I were irresponsible I would just blow it off and not care. But if I wrote down the wrong number I have a responsibility to get a hold of this person. This extra work combined with wondering if it’s the right number, leaves a bad taste in my mouth.

You’ll want to have your office hours in the voicemail so that cleaning customers know when they can connect with you. You don’t have to always be available during all of those times, it’s just the possibility you’ll actually pick up your phone or will be able to give them a call back during those hours. Adding in office hours makes your business sound much more professional. It’s the sign of a more established, well-run company to have business or office hours.
"Voice mail has lost its appeal primarily because it's very much tied to the notion of the phone and your communication being tethered to a physical thing or a physical location," he says.