[Redmi Note 8 Pro ROMs, Kernels, Recoveries, & Othe] psychofad:
So until last night I was still running the Bliss Rom Android 10 CFW Rom, and I recently had to switch plans since I had been on someone else's plan until they recently needed to switch due to less income and a better plan price....anyways, so I signed up for Red Pocket and chose the GSMA plan since according to the IMEI checking page I could sign up for either GSMA or GSMT and well you got 2x the data on the GSMA...why not right? Well, living under the rock as I have been, no one there said anything about this AT&T whitelist, and of course I only started noticing anything about it after I had already paid for the first month and was awaiting the sim card to arrive via snail mail. So I get the sim, put it in, complete the activation and number transfer and after receiving the e-mail saying the number transfer was completed I turned on the phone to test it out. So, I have been on T-Mobile for the last like decade, and sure when I was working in a warehouse I rarely had a signal, but once I was connected it was fairly fast, and at home It was great, if the internet in the house went down while I was streaming a show, I would just pop my phone out and turn on my hotspot and continue, this clearly was not the speed I was seeing from AT&T however, but ok, well while I was playing with the internet, I received a text from my dad and I replied back, he got it and replied to me. So I try to call him, and the dialer doesn't even ring, it just sits there for a few seconds and then I see "call ended" on the screen...yup not on the AT&T whitelist, furthermore, I noticed that the VoLTE setting was on but greyed out and the icon was never showing up. So for the next couple of days I tried to see if there was some way to enable it but after many hidden menus I finally resigned and just called and had Red Pocket send me a sim for GSMT so I could switch and they were very helpful and with a small wait on hold while the rep got the approval to switch over (I wasn't the only one calling for this reason) the new sim was on its way.

That is the backstory, so all this messing with the phone got me back on here to see all the progress that had happened since I had first unlocked and rooted my phone and I decided I would backup everything and update to Android 12.1 since I was still on Android 10, start the new service off with a new OS, So I updated to MIUI 12.5 then from there I used the 12.5 Recovery and loaded up EvolutionX since I read so many positive things about it. OK, heres the funny part, suddenly, I notice the VoLTE icon is lit up, no way, could it be? So I figure why not, I haven't switch the sim out yet, so I try calling my dad, and it rings, and he answers....WTF! So apparently, EvolutionX fixes Redmi Note 8 Pro so that it works on AT&T again! Awesome jobs Developers! I bow down to thee! Maybe you could add that to the OP, bypasses AT&T whitelist, you're welcome! Sorry for the wall of text, I felt it was necessary to build the backstory, I will still be switching my sim to T-Mobile, The 4G tower was closer to my home and I never had any issues with their service except at work in the warehouse where no one should be on their phones anyways since well, you're at work.

TL;DR

If you own a Redmi Note 8 Pro and were on AT&T and have been affected by the recent 3G shutdown, consider flashing EvolutionX so you can continue to use AT&T as IMS Registration is able to complete and it fixes VoLTE so you can send and receive calls again!