Tip: If you are a larger business and this is a voicemail that pertains to the general business number, then you want to sound professional and provide as much information as you think is necessary for a potential client. Usually, the company website URL or the company email is a good way to get the customer to contact you through other means.
The voicemail function allows the caller to leave a message in case you are busy. It informs the caller of your status and assures that the message will be heard. For instance, good voicemail greetings at corporate firms create a pleasant impression on the caller’s mind or a hilarious voicemail can make someone’s day.

In case you avoid answering phones at your desk, have a voice message ready. When recording such a message on the phone, keep it short, sweet, and to-the-point. If you are working at a place where direct interaction with clients is required, you might get pesky calls or bulk messages (e.g., orders, requests, contest-entries, etc.).
For those with voicemail greetings that get changed about as often as a new president is elected, know that this is doing a serious disservice to the caller-recipient relationship. It signals to callers that the business is anything but an authority, most likely not very detail oriented, and has questionable overall credibility and competency. Those aren’t traits that any business wants to associate itself.