I’d bet good money that most voicemails never get played. Instead, they just sit there serving as extra “missed call” notifications, letting you know to call or text back whoever bothered to leave you the message in the first place.
If you don't create call answering rules, incoming callers will be sent directly to your voice mail when you’re not available.

When recording a personalized voicemail greeting on your office phone, your greeting should include only the company name and your extension number. When recording a personalized voicemail greeting on your office phone, your greeting should include only the company name and your extension number. State your name and spell it out if you’re asking callers to follow up with written correspondence. State your company name and department name. Let callers know that you cannot take their call right now. Invite them to leave a message. What should I record on my work voicemail?
The telephone systems have the feature named as Voicemail. VoIP is the best example of it. When a receiver is unable to pick up the phone, then the caller can leave the voice message on the receiver’s phone. In older telephonic machines, such messages were stored as a voice message directly, and the receiver can hear them later. In modern telephone systems, such info is being stored on the server of the service provider in the user’s mailbox. It is similar to email in which the messages are saved in the form of audio instead of text.