Never use voicemail as a way to avoid speaking with someone. It doesn't help, and a person would have to be terminally dense not to figure out your game. If you must call when you know the other person isn't available, say, "I know you won't be able to take the call now, but I wanted to let you know that..."
Remember that the speed of your words can negatively impact your message as well. "If you have to rush to get a message into the amount of time allotted for a voicemail message, you’re saying too much," DeCesare advises. "Say less and slow down. You want them to feel that talking to you will make their lives less stressful. If you're frantic and mumbling on the phone, it gives them a foreshadowing of what it will be like to work with you."

If someone is listening to your voicemail greeting it's only because they intend to leave you a message. Don't make them listen to 3 minutes of rambling in order to do so. Plus, you're more likely to deliver a clean, professional read if you stick to shorter greetings. If more specific information is needed, direct callers to where they can find it on your website.
When opening your voicemail, start with a professional or generic greeting like, “Hello” or “Good Morning”. Be sure to clearly state your name, who you are/where you’re from, and (where applicable) how you got their contact information.