Is it possible to recover an old voicemail message?

I have an iPhone 6s, it's running iOS 12.1. It is no longer connected to a cell service. Sometime around mid-2018 I had a voicemail message left on the phone from my grandfather. I'm assuming it's obvious what the reason for why I suddenly want to recover this voice message is. If I go to the voicemail on that phone it says "to retrieve a voicemail first set up a password and a greeting" and when I attempt to do that it says "voicemail unavailable."

I wanted to save it when it was left, but it was pre screen recording and I didn't know how to go about that. Is there any possible way I can recover it, or do messages get deleted after a certain time or aren't recoverable from a phone with no cell service? If I temporarily put the SIM card for my current iPhone in it might that work?