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.
Voicemail transcription (beta; available only in certain countries or regions) shows your messages transcribed into text. Transcription is limited to voicemails in English received on your iPhone with iOS 10 or later. Transcription depends on the quality of the recording.

Voicemails don’t necessarily have to be monotonous or extremely jazzy or funky. What you’re looking for is a balance between the two. Whenever I call someone and their voicemail greeting is playing, it tells me a lot about who they are, as a person. Which is why, you’ve got to put a little bit of “you” when it comes to voicemail. And the best part about all of this is, since you couldn’t come to the phone, at least the callers are having a good time listening to the message.
Go to Settings > Phone > Change Voicemail Password. You can then follow the prompts to change your Voicemail password.