While recording a message, make sure that you don’t yell into the phone and make sure you record in a quiet place. Setting this up in a restaurant will make your iPhone voicemail greeting sound like you are actually picking up the phone.
A word of warning: These greetings will not do you any favors if you're in the midst of a job hunt or work in a conservative industry. Always remember your target personas. If there's a chance they won't appreciate your sense of humor, opt for a straightforward greeting instead.

The voicemail greeting is an important element of your business’ phone system because it is often the first impression of your business that customers will have. Creating a really good voicemail greeting is a unique opportunity that you can use to impress customers by putting your best face on, while increasing the chances that you’ll retain their business in those times when you can’t
For personal users, a funny iPhone voicemail message may be just what you want. It’s still a good idea to keep it short, but you can have some fun by using your iPhone to record a funny voicemail message played over a speaker on your computer or another device.