[Samsung Galaxy S7 (Exynos) ROMs, Kernels, Recoveri] phazei:
So, I ended up wiping and doing another clean install. This time before the first boot I installed the XAA->TMB. Then it booted for the first time, but before I could begin the initial setup, I got a message "Service Provider Update" about needing to restart due to new features in the SIM. This rebooted into recovery every single time I rebooted. Then I found I needed to disable the service "com.sec.android.AutoPreconfig" via ADB. After that it booted up and it mostly worked. HotSpot worked, VoLTE said it was on, but when I went to enable WiFi Calling, it would turn on then immediately turn off.

Then I went back and flashed the TMB stand alone (non-multi) CSC. Rebooted, was back to the T-Mobile branding, missing quick launch buttons, and no bluetooth tethering. So I found "CSC Feature Expert" which let me play with all the settings easier than manually editing the xml's. I did clear the list for the quick settings and rebooted, but some must just not to be included at all in that CSC. So then I backed up the /system/csc folder so I can compare it later.

Next I flashed back to the XAA->TMB multi-csc. This time the WiFi Calling did connect. All the other options are back to. Only thing it's missing is a toggle for the WiFi calling in the Quick Settings menu, which I can live without. The VoLTE setting is in the phone settings and not in the system settings with the multi-TMB vs the stand alone TMB.

I also tried replacing the /system/csc folder with the backup I'd taken from the stand alone TMB. When I did that, the bluetooth tethering went away and the HotSpot settings became T-Mobile branded again, but I did not get the WifiCalling quick setting toggle, so that doesn't seem to be added by anything in the XML files for the stand alone TMB that I can tell. So I just went back to the /system/csc files from the multi-csc.

TLDR; of me getting WiFi and VoLTE working and not losing lots of quick settings and blutooth teathering with TMB was, using CSC Select 2.4.5, install SuperMan (no reboot), install XAA->TMB, reboot, disable "com.sec.androidAutoPreconfig", setup phone, install stand alone TMB, reboot, make sure wifi connects, install multi XAA->TMB. whew!

Hope I don't break anything and have to start over again! :fingers-crossed:

EDIT:

so, with all that, I didn't actually test making a call... just that it could all be enabled. So I just tested the actual calling....

WiFi Calling:

When making a call with WiFi Calling, it starts the call and rings, but the on a call page closes so it doesn't actually show it's on any call. The call itself is in progress, but the phone doesn't indicate it anywhere. If I attempt to initiate another call, it blinks to the calling screen but nothing else happens, the current call continues. Only way to hang up is to put the phone in airplane mode.

VoLTE calling:

The phone shows the dialing screen for just an instance then goes to a call ended screen and then back to the recents page

Regular calling:

works!

Also would like to note that I'm on StraightTalk with a T-Mobile SIM card. StraightTalk indicates they support VoLTE and WiFi Calling (need to register on a site for the wifi calling to link) While the results were all the same I tried multiple combinations of settings:

I tried it all with the multi-CSC TMB as well as the stand alone TMB CSC.

I also tried it all with both the T-Mobile APN and StraightTalk APN settings with the combinations of CSC's.

I also tried it with Google Voice on and off on the stand alone TMB CSC.

So I guess it probably just isn't going to work... I guess that's ok, I hardly ever talk on the phone, and when I do make calls it's most often through FB Messenger.

Oh, another observation, the video calling in the dialer only shows up when using the stand alone TMB CSC.

If I also copy the files from multi-CSC TMB /system/csc folder into that folder when the stand alone TMB CSC is installed, the video calling does away, but the bluetooth tethering comes back, so that's possible to add via the xml files alone. The other missing quick icons do not come back (record screen, screen shot, data saving, cast, sound, maybe another I didn't notice) which only existed in the multi-CSC TMB.

EDIT2:

Ahhh, I broke it all. So I was all done testing and just going to go back to XAA->TMB and leave it at that. So I went back to CSC Selection like I have some dozen or more times already, and tried to flash it, but nothing. It said it finished but the log screen just said EFF backed up, but nothing else. I tried a few different CSC's, same thing. Now I'm CSCless :o

Booted the OS and phone Info just shows blank for all the CSC info, and the settings menu's super wacky (attached). Actually a couple more reboots and it let me flash it again. I'm done!