Native Samsung Visual Voicemail app on unlocked model with T-Mobile?

I'm thinking about getting the Flip but want to confirm this first. Can anyone help me confirm whether the native built-in visual voicemail works and whether you're using the T-Mobile or unlocked model? To be clear, I'm referring to the native Samsung app that looks like this and this, NOT the T-Mobile branded app that you download from the Play Store.

I've seen some videos of the phone where the app was visible in the app drawer, but there was no SIM and I'm not sure which model they had. And looking at past posts regarding other Samsung phones, it seems to be very hit or miss, so I'd like to confirm before ordering.