How to use AT&T wifi calling on an unlocked phone?
So I currently have an AT&T plan with an AT&T LG G4. I just bought an unlocked Galaxy S8 from Samsungs Website, planning on using that to update my current AT&T line. After I bought it, I was reading up on unlocked phones because i didn't know much other than you can switch carriers if you want to (But i'm not planning on doing that, I just bought it because it was $30 cheaper than the ATT-version, plus it came in a color that wasn't available from the ATT-version. I came across many fourms saying that services such as Wi-fi calling wouldn't work with an unlocked phone on AT&T, and that stressed me out because I use that service a lot for texts in my work building b/c of spotty cell reception.
I'm confused though because I called up AT&T and asked if i'd be able to use Wi-fi calling on this unlocked phone, and they said I can. They just said that i'll have to 'update the device information with the new one and set up the features on the device'. They also said the only situation that might affect the service is if the device is 'blacklisted', but it wasn't, so they said I'd be able to use 'all my services if the device information is correctly updated in our system'. I asked again for clarity if I can bring this unlocked phone to an ATT store and they can update my line and still be able to use Wi-fi calling, and they said that's correct, you just may need a new SIM card.
I'm confused because nowhere online in my research did I find anyone who was able to use unlocked phones with Wi-Fi calling, but those articles were at least a month old, so maybe they changed their policy? I made it as clear as possible what I was asking.