Most cell phones show the number and voicemail duration when a call is missed. So if the recipient sees the message is from an unknown number and only a few seconds long, they'll assume it's not important and hit delete. Since the message doesn't appear to be substantive, they're not prompted to listen.
However, I would not leave a voicemail until I had called that hiring authority many times. Only after I conclude that it is unlikely that I'll ever catch this person, would I leave a voicemail. The script for leaving a voicemail is not much different from the script for a live conversation: “Mr./Ms. Smith. My name is Sally Jones. My phone number is . I'm a recent college with a degree in _________. I'm offering hard work, determination, passion and commitment to an excellent employer like you. I would like a chance to meet with you. Again, this is Sally Jones and my phone number is . Please call me; I'd like to meet with you at your earliest convenience."

3. Click on your phone, then “Scan,” if you’re prompted to confirm what type of data to scan select “Voicemails.”
People tend to remember the first and last events of the day. Now, you could make your sales calls in the morning, but nobody wants something else on their plate when they’re just starting their workday. By waiting until the end of the workday, though – traditionally, around 4:30 p.m. – you won’t be competing with other distractions, and you’ll be one of the last things that happened to the contact while they were at work.