I know you're out there. I know that you're afraid. You're afraid of us. You're afraid of change. I don’t know the future. I didn't come here to tell you how this is going to end, I came here to tell you how it’s going to begin. I'm going to hang up this phone, and then I'm going to show these people what you don’t want them to see. I'm going to show them a world, without you. A world without rules and controls. Without borders or boundaries. A world where anything is possible. Where we go from there, is a choice I leave to you.
The bottom line is that a business’s situation is likely to change often and rapidly, each of which need a unique and applicable voicemail greeting to cover the circumstances and timeline. For example, callers shouldn’t reach a business-as-usual voicemail, and therefore expect a return call within the business day, if the subject they’re calling is out on vacation for two weeks. Such a lack of communication is a recipe to lose that caller’s trust and tarnish the brand’s reputation.

When leaving your voicemail and phone number, do not say, "Please call me back at ..." Nothing sounds more like a salesperson making a cold call then saying, "please call me back at...".
“Greetings, this is Science Officer Spock. Currently there are no lifeforms available to take your call but at the pre-arranged audio signal, please feel free to leave any verbal communication you feel is necessary. Live long and prosper.”