What I just tested while on a call was to turn off Wifi and try to surf the internet or watch Youtube and nothing would work. My friend said this is what happens with no VoLTE...just like the olden days of Verizon and Sprint. I believe AT$T had VoLTE before them. Also, while on a call, the call dropped once and the connection is certainly not as clear sounding as my Note 9 that was an AT$T branded device. Also while on the call, the service dropped down to "H" which I assume was HSPA+. As soon as I hung up, I then again saw the LTE logo. Great..sucks! I knew I'd be having issues with an Unlocked phone and my AT$T SIM card but not this level of crappiness. I'm going to see if I can flash the AT$T firmware/bloatware tomorrow to see if that does the trick. Otherwise, I'll be returning this Unlocked (and forfeiting the $600.00 trade-in and I guess now the $200.00 credit voucher for Samsung.com).
AT$T just sucks. I read a lot about this beforehand and seemed confident that flashing the ATT firmware will do the trick. I hope that I also don't have to call ATT customer service to try and get them to provision something else on my phone service to get a feature working. I really need wifi calling/VoLTE. UGH!