I have never used wifi calling but understand where it may be useful. I've seen a few threads where people say the carrier controls that feature on unlocked phones, so a caveat of an unlocked phone and more games the carriers use to leverage sales.
I have an unlocked S10 Lite and strangley enough, before the UI 3 update yesteday I did not have wifi calling as an option, and now I do. I am also on AT&T. I had to first agree to acknowledge calling 911 limitations and confirm a home address for calling 911 then got a text from ATT saying it was activated (I hope I don't get charged), and now my wifi calling option is toggleable.
I've also had no issues with visual voicemail or call quality, but I know what it feels like when an update completey jacks up your phone so I believe it. There are so many variables among device models, what's installed on the phone, carriers, locked vs unlocked, that it seems a matter of luck when you get bit and often a long time for it to get fixed if it wasn't something that was purposely taken away...sometimes makes me nostalgic for the simple flip phone days where I didn't live in fear of updates!
I have been working with Google support since the phone arrived and they have been 0 help.
if I can't get this working then this phone is being returned. Samsung charges a premium for these phones and basic functions don't work. Such a shame.
Check and see if it is enabled.
Settings | Connections | Wi-Fi Calling
Right is on, Left is off. This option will be under Wi-Fi and above Bluetooth, unless it has been disabled.
AT&T appears to be rolling back it's decision on WiFi calling, there was a second update in Janurary that appears to only have been sent to unlocked device holders that is enabling this feature. It may have just not gotten to you yet, as AT&T decides how and when to roll these updates out.
Yeah, I would not reccomend that... Google Fi is supposed to support WiFi calling on unlocked devices from my understanding, so not sure why it was disabled. Also do not know how AT&T is enabling it remotely, but several users here are stating that it is magicly back after the second Janurary update.