@umbra21 - It's not jokes that annoys me so much as someone who leaves a message ten minutes long, particularly when you have to wait out the whole thing before you can leave your voicemail.
Even in today's fast-paced world, customers don't like being greeted with an automated message. According to the New York Times, callers of a certain age are put off entirely if they are answered by a voicemail instead of a real person.

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 way all your words and sentences come together gives your script a distinct written tone. Combine that with a specific speaking tone to create an on-hold message that reinforces your brand and product set. Selecting the correct tones will ensure your intended message is communicated effectively. If your target market is the younger generation, then a tone which embodies fun and excitement would be most suitable.