I have the Unlocked Note 9 512GB as well, the Voicemail app was already installed on my phone. Which you won't need to dial to hear the voicemails and you can just check through the Voicemail app on the list with phone numbers. It won't transcribe any voicemails.
I am using the unlocked phone on Verizon, bought mine unlocked from Best Buy for the trade-in promo and gift cards as well.
So if the screenshots are what you are looking for then the app should be on phone.
I first thought it would have been something I would lose than when I received a voicemail got the notification from the app.
I did not restore any applications from play store or Samsung. I reinstalled them as needed, so wasn't an app that was restored and was already on phone. So not sure if it was that it detected a Verizon Sim and automatically enable some apps or this app already came with phone.
If this is not it then sorry but like I mentioned I the last time I used it, it looked like this. But if it is hope it is there.
Update:
But if you do pay or want Premium Voicemail, that would not work on this version as it is not a verizon app.