On your Android device, open the Google Voice app .At the top left, tap Menu Settings.In the Voicemail section, tap Voicemail greeting.Next to the greeting that you would like to use, tap more Set as active. To change your voicemail greeting: Go to Phone > Voicemail and tap Greeting. Then follow the prompts to change the greeting. To change your voicemail password: Go to Settings > Phone > Change Voicemail Password and then enter the new password you want to use.
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.

Alternatively, you could try disabling call forwarding, though your particular carrier or phone model may not allow it:
It works similar to the old answering machine, with the only difference is that the old answering machine will store the voice message in the machine itself, while your phone’s voicemail system will store the voicemail in your service provider server. You can also forward the voicemail message to someone else’s mailbox.