However, some cellular service providers allow users to access and update their voicemail by calling their own numbers from working landlines or phones on other wireless networks, so users whose accounts include such an option and who have access to alternative service could keep the voicemail greetings updated even when their own mobile phones cannot connect to cellular or internet service.
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.

By having the alternate greeting pre-recorded and assigned, you can change your voicemail greeting on the fly. Recorded Name: Set this option to play a recording of your name instead of a greeting. “Leave a Message” Prompt: Check this field to play the following message after your greeting: Please leave your message after the tone.
If you choose not to record and transmit a greeting through your phone’s voicemail system, you can utilize a visual voicemail application that has been installed on your phone instead.