Enter a name for the new greeting and then tap Save. Change your greeting. To use a greeting that you've already recorded or switch back to the default greeting: On your iPhone or iPad, open the Voice app . At the top left, tap Menu Settings. In the Voicemail section, tap Voicemail greeting.
Some cell phone service providers allow users to access their voicemail accounts via external methods such as landlines, and those users could keep the voicemail greetings updated in the absence of cellular and internet service.

But now I'm going to go ahead and record. So press record sorry I missed your call. Please leave your voicemail after the beep and I'll call you back. Thank you. Press stop and now. I could press play and then if I don't like what I hear, I could press record one more time and when I'm satisfied, I could press save on the top right and it's going to save my greeting and that's all I have to do to set a new voicemail on my iPhone. You could always come back to this page. Press record one more time and replace your voicemail here. You're greeting here, and you should always use someone else's phone to call to see how it sounds from a different device.
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.