To create a greater sense of authority, and that you are somebody important, list the name of a person and company who you've worked with before, especially if that person and company is a direct competitor of the person you are calling. Nothing grabs the interest of the person you are calling faster than hearing the name of their main competitor.
The basic rule of thumb is that callers should hear one of two things when they first connect with your voicemail — either an apology for not being able to answer the call or a “thank you” for having called. You can do both if you prefer, but keep it short and to the point.

Your voicemail greeting can make a positive or negative impression on people. By considering your target audience and tone, you should be able to keep it positive. Length: Don’t make people wait minutes to leave a message. Apologies: If people expect your to be available, apologize for missing their call. Set expectations: Let people know when they may receive a callback, but be realistic. Accuracy: If you change your voicemail for things like holidays, be sure to update it when needed. How do You Set Up a Business Voicemail?
2. If you’re out of the office: “Good afternoon. You have reached the office of [your name]. I will be out of the office beginning on [date] and will be returning on [date].