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.
You can ask your admin to change the greeting language for everyone in your organization. Your admin should see this topic for instructions: Change the default language for greetings and emails.

While it is understandable that not everyone likes to use the default voicemail greeting messages on their devices, there is a simple and quick way to alter the voicemail greeting on the Samsung S20 from any carrier (including Verizon, AT&T, T-Mobile, Spring, and others).
To set up Visual Voicemail, tap Set Up Now. You’ll be prompted to enter and confirm a voicemail password. Next, you’ll have the option to choose the default voicemail greeting or record your own. If you want to record your own custom greeting, tap Custom. Once you’ve entered created your password and chosen your greeting, you’ll be able to receive voicemails and view them in the Phone app.