Anyway, the below information was copied from the Verizon Wireless website. I assume the other carrier's have a similar feature.
---Is there a way to access my Voice Mail messages without having to enter my password each time?
Yes, you can reformat the Voice Mail number on your phone to automatically include two pauses and your password. Once you’ve made this change, you won’t have to enter your password to listen to your Voice Mail messages.---
Source:
https://forums.imore.com/e?link=http...token=r8d9VmYC