A secretary in a doctor’s office creates a voicemail greeting that says, “If you have a scheduled meeting with us, we could use copies of all your medical documents from last year, so come prepared.” Using the word “could” gives patients the impression that they don’t necessarily “need” last year’s documents. See the difference between “could” and “need”? Your word choice can impact a future meeting significantly. If you want a customer to perform a specific action, you need to pay close attention to how you express your calls-to-action.
Here, the ophthalmologist is not in a position to receive a call. However, he/she makes sure the patient’s need is addressed.

Here’s a generic business voicemail greeting example: “Thank you for calling [company/person’s name]. We are currently unavailable, but if you leave your name, phone number, and message, we will get back to you as soon as possible.” The above greeting is a professional voicemail script used by many growing and established businesses.
Here's the problem with recording elaborate joke messages on your answering machine: Your answering machine will become more popular than the person who owns it. Friends would tell total strangers to call my number and listen to the new goofy message. They would become disappointed if I actually answered the call first. I would have to hang up and let the machine pick up just for other people's entertainment. Dozens of people were finally calling my home phone, but few of them wanted to talk to me personally.