I am facing a strange problem with my S21 Ultra Unlocked which was directly bought from Samsung. I had enrolled into OneUI 4.0 beta when I was in the US. I was using Sprint connection then. I could see that, 'Service provider software version' is mentioned as SAOMC_SM-G998U1_OYM_XAA_12_0025 XAA/XAA, VZW/XAA.
I had to travel back to my home country (India) and I am using an Airtel sim card (LTE) here. Now, the strange problem is that LTE works here fine. But, VoLTE is not working. The network changes to 2G for phone calls. I am assuming that the autoswitching bands which was introduced in OneUI 4.0 is causing the problem here. I think since my software version shows as VZW, it's not registering the GSM bands.
Can anyone please help me here? The 2G network in my area is really bad and the calls get dropped quite often. I read some posts that we had an option to change local CSC in the older software, but it's not allowed anymore in OneUI 4.0.
I guess reverting to OneUI 3.1 will help, but that means a hard reset and again, I am not sure what is going to happen after the OneUI 4.0 stable release is out.
All I can advise is that you reset your device network settings in Settings > General management > Reset > Reset network settings.
I'm also running the One UI 4 beta on my S21 Ultra, but I'm not facing network switching issues.
Thanks for the quick reply. I reset the network settings already. It didn't help. I read somewhere that the autoswitching networks could be causing the issue. Are you on Verizon network?
Looking at my software version, I think only the CDMA bands are active. I am hoping that Samsung can help. Maybe they registered me under Sprint/Verizon when I registered for OneUI 4.0. They might have to change something to switch to a GSM network.
I use it to force LTE because 5G in California lowkey is not much better than a donkey's rear end.
I tried to do that as well. The problem is when I check my IMS service status (*#*#4636*#*#), it says IMS Registration as Not Registered. Hence, Voice over LTE and Voice over WiFi are shown as Unavailable.
An update to the issue:
Using Smart Switch PC, I rolled back to One UI 3.1. VoLTE and WiFi calling started to work again. But, soon after I got update notification for One UI 4 beta. To confirm that it is indeed an issue with One UI 4, I installed it again. And as expected, I am not getting VoLTE or WiFI calling again.
Since I changed from Sprint to Airtel, I am not able to withdraw from the Beta program as well. I am getting the error "One UI beta features aren't available because your service provider has changed".
Also, I am not sure what the final One UI 4 will offer. For the first time in my life, I am seeing an Android upgrade causing my phone to not able to connect to VoLTE.
EDIT: I am also attaching the screenshots of Phone Information. As you can see, in OneUI 3.1, VoLTE and WiFi calling are provisioned. But in OneUI 4, both are not available.