You might also consider giving them the option to skip your voicemail message completely by pressing another key (again, check with IT). You also want to make callers aware what you will return their call, instead of telling them that you will try to return their call--and let them know when you are likely to do it, if possible. If necessary, provide additional or emergency information in your voicemail greetings. My dentist, for example, lists his cell phone number for emergencies.
Education Details: Users and departments can customize their extensions with their choice of music, messages, and voicemail greetings. Keep your callers on the line with professionally recorded messages on hold. Keep callers engaged by answering frequently asked questions, such as business hours, locations, or directions.

Voicemails need to maintain a professional consistency that’s aligned with the entity it’s representing. That said, the structure can vary depending on the situation. There’s no template set in stone. In fact, trite and generic should be off the table. The goal should be a balance of uniqueness and practicality.
The business answering machine greeting you use should be fairly short and to the point, though you can use it as a way to demonstrate what your business has to offer. Your overall tone in the message should be professional and indicate to callers that though their call has been missed at that moment, they are important and you plan on contacting them as soon as possible. Within this, however, you should not indicate that you are talking to someone more important than the caller. Your business answering machine greeting should also be customized in any way you deem appropriate for your business and needs. Jotting down the greeting will prevent mistakes when recording it.