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.
Call in any office during working hours, and be sure that you would be connected to a voicemail. Voicemails have become an important part of our lives, and help us stay connected even when we are not there to answer a call. More and more people are gradually realizing that their voicemail greetings play a large part in getting business and leave a positive mark on the customer. If you really want to record a professional voicemail, make sure you sound professional while you record it and never leave incomplete messages.

Just in case you fall victim to mumbling or speaking softly in your voicemail message be sure to repeat your contact information at the beginning AND end of your message so that the listener is more likely to be able to pick up on the information. This helps if you are speaking quietly or if the listener was not ready to record your information when you said it the first time. Repeating your information will save the listener time as they will not have to listen to your message again to get those details.
The above section details types of phrasing to avoid; however, it doesn’t detail what users should NOT say on their greeting. Though this is a bit loaded, as there are hundreds of combinations of things one shouldn’t say, there are some key components users should ALWAYS avoid. a. Forget About Slang: You should strive to be as professional and welcoming as possible in your greeting. While this may steer you towards using slang, in an attempt to make callers comfortable, it’ll most likely work against you. As a professional, your demeanor, tone, and speech should be clear cut and well articulated. Using slang undercuts this and works against you. b. Don’t Even Think About Profanity: This is a no-brainer. Never, under any circumstances, curse in your greeting EVER! c. Keep Your Sentences Clean, Don’t Ramble: Introduce yourself and give your caller specific direction. Avoid long diatribes detailing tangent thoughts. Keep it simple and quick. d. Always Return Your Calls: It’s important for callers to feel they are valued. Nothing dissolves this quicker than a greeting that doesn’t stress this. For example, “I’ll call you when I can,” “If I don’t return your call, please call back”—these phrases are terrible and completely destroy any good will you may have with a caller.