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.
Website: https://www.republicworld.com/technology-news/mobile/how-to-set-up-voicemail-on-android-learn-to-change-your-voicemail.html

To call your voicemail on an Android phone, simply open your phone’s dial pad and hold your finger down on the “1” key. You can also call your voicemail from a different phone by calling your own number and tapping the pound key. Navigate to your voicemail option if using a cell phone. … Listen to the recorded voicemail instructions. … Press the number on your keypad symbolizing “Yes” when asked if you want to delete your current message. … Select to record your own message if you want, or leave it as the mechanic default message. Step 1: Press # Right after you realize you want to delete your voicemail press the # symbol. It is VERY important that you do not hang up the phone. … Step 2: Listen to Menu. Once you press # on your phone, you will automatically be given access to a menu.
Listen to and manage your U-verse Voicemail messages by phone or online. Dial *98 from your U-verse home phone, dial your home phone number from another phone, or access your voicemail messages online from the Voicemail Settings tab. Press the * key when you hear your greeting. Enter your PIN. Press 4 and follow the prompts.