As mentioned above, alerting callers that they won’t be getting an immediate call back is of upmost importance for an entity’s reputation and a caller’s satisfaction.
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.

At present, you have to record your greeting by recording directly into the iPhone microphone -- the results of which are average, of course.
Congratulations! You've recorded a professional voicemail greeting that your callers love. If you want them to keep loving it, you'll need to update regularly. Adding seasonal information and varying your message keeps your greetings fresh, which is especially important for businesses whose clients and customers call in on a regular basis.