What’s more annoying than being unprepared? Doing business with someone who is. In other words, don’t wing it — practice your script, speaking slowly and annunciating each word.
iPhone users have another option: You can send a voice message from Apple's Messages by tapping the microphone button inside the text box (this works only when you're messaging other iPhones). By default, these voice messages last for only two minutes before they are deleted, but you can change that. Either tap Keep under any sent voice message or go to Settings > Messages and tap Expire under Audio Messages. You can set the expiration date to Never, but this affects only your record of the conversation, not the recipient's.

Because you never know the quality of someone’s phone audio or your cell phone service, it's not a bad idea to give your name and phone number twice within your message. The thought being, if the person you called can’t understand who you are or how to call you back, how can they be expected to return your call?
While email and text support saw an increase in recent years, many customers, partners, and potential hires still prefer to call your company directly. When writing your voicemail script, include basic information such as a short greeting, your company name, an invitation to leave a short message, and the time frame in which the caller can expect a return call. If relevant, you may want to include your office hours, extensions for company departments, and the contact information for your office manager or HR department.