Ok. I found this.
AT&T also does not allow WiFi calling on non-branded phones.
https://forum.xda-developers.com/galaxy-s8/help/samsung-s8-unlocked-phone-wifi-calling-t3622318
As for Visual Voice Mail. It is a paid service on Verizon so you have to have it as one of the options in your plan. I believe it costs $2.99/month. You also would need to install the Verizon's Visual Voice Mail app.
Video calling SHOULD work. It's built into the default phone dialer app on the device. As long as you have LTE connectivity you should be good on that.
I don't get voice mail notifications on my Verizon branded S8+. I will have to see why.