Built-in video calling option missing for AT&T

[TechieSophie]

I have AT&T as my carrier. They have been trying to get my phone to be able to do video calls with the phone app (as opposed to using Google Meet), but my phone is missing VoLTE setting toggle in the Mobile Networks setting. AT&T said they've tried to push updates to my phone to fix this, but they're unable to do so because Samsung did not allow them to be able to make the changes to my phone. Why am I not able to configure VoLTE on my phone? Please help me fix this! I'm supposed to have this feature on my mobile phone plan. The rest of my family members with phones purchased from AT&T on the same plan as me have the ability to do video call from the Phone app, but not me, because my phone has been purchased from Samsung instead of AT&T.  My Phone app defaults to Google Meet for video calls, and I'm unable to select anything else. AT&T said my SIM has been provisioned for video call, but the VoLTE component is missing on my phone's mobile network, and they haven't been able to manually push it to my phone, and the problem is on Samsung's end. 

[Ekamek]

If AT&T sold you the phone or it's active on their network, they can make whatever changes they want to. If they can monitor everything you do with the phone on their network, they sure can modify any software. They modify the firmware before pushing it to their customers, right? That's some bunker excuse from a service provider.

Defaulting to Google Meet is Android-wide, though. I used to do so on T-Mobile with stock dialer, but it was switched to Meet some months ago. It's probably a year now.

[TechieSophie]

No, the phone was purchased from Samsung and AT&T had worked with me all afternoon today to try to push the video call feature to my phone, but they were not able to get the SIM to overwrite the native Phone app to include the video call feature. Everything they tried failed to make any changes.

[Ekamek]

You can install AT&T firmware on it, start by installing AT&T U1, then AT&T U firmware, and the video calling option in the phone dialing app will show up. This is, of course, if you're willing to live with AT&T bloatware.

[TechieSophie]

Where is a safe place to download and install this firmware? XDA Developer?  It's been a long time since I've rooted and installed custom ROM on my phones.
I asked AT&T if they could install their ROM on my phone, but they didn't. It's probably because I didn't purchase my phone from them and they didn't want to be held responsible if somehow the installation fails. I've soft-bricked a phone once when installing a custom ROM, so I know how things can go wrong.

[Ekamek]

I use sammobile.com or samfw.com. samfw.com doesn't require an account, and it's faster to download from them. XDA Developer is an option but not sure if they host ROMs anymore. I have not used XDA for download in a couple of years. BTW, XDA has a good step-by-step guide on how to flash using Odin as well.

[TechieSophie]

I'm definitely going to need a refresher on using Odin to flash the ROM. Thanks!

[Ekamek]

I find sammobile.com instructions better, though.

[TechieSophie]

Noted. Thanks again!

[LongHiker]

@TechieSophie I'm going to guess that you bought an unlocked phone from Samsung and that the others have AT&T locked devices. 

AT&T has a history of somewhat neglecting unlocked devices. They are indeed in control of the menu where that setting would appear.