If anything big changes- address, phone, etc.- make sure you correct your voicemail early on. Keep It Short; We know, we know. We just gave you all this information and we’re now telling you to ‘keep it short‘. But, a professional voicemail greeting (or any for that matter) shouldn’t go beyond 20-25 seconds.
Your voicemail message should ideally answer all of the following requirements: Brief -- nothing bores callers as much (or makes them hang up as often) as long voicemail messages; Informative -- if it's your professional voicemail, say your name, business, and if necessary, department. Let your callers know when to expect a return call

What kind of business phone service does your company use? If they haven’t been updated recently, or you haven’t made the switch to a higher-end VoIP phone that typically offers better sound quality, it’s time for an upgrade. The equipment you use can make all the difference. At the end of the day, people are judging your business based on little things like that.
If you want them to leave a voicemail, tell them right from the beginning, “Please leave your name, reason your calling, and the best way to contact you.” If you want them to call you back during normal business hours, tell them, “Please call back during normal business hours.” If you want them to call back prepared for a lengthy conversation, you can say something like, “Please refer to our website’s FAQ page,” and then provide the URL. Self-service should never be underestimated.