Most of the time, an update to your carrier’s voicemail app or settings will cure the issue; however, it is important to confirm that your voicemail number is appropriately configured before proceeding any further.
To use a different greeting you already recorded or switch back to the default greeting: On your Android device, open the Voice app . At the top left, tap Menu Settings. In the Voicemail section, tap Voicemail greeting. Next to the greeting you want to use, tap More Set as active.

Need to change your voicemail greeting on the iPhone? If you never recorded one and want to record or change a voicemail greeting, you've come to the right place.
5. When you're ready to begin recording, tap on "Record" and begin speaking. Once you begin recording, you'll see the line turn red. This indicates how much time you have left.