Question VoLTE issues

[1075dn]

I have a Sprint Galaxy S8 that I paid someone online to network unlock, however it’s still running the original Sprint firmware. The device officially supports VoLTE, but in Settings->About->Status->SIM status, IMS says Not Registered, and all calls downgrade to 3G. That’s going to become a problem soon since 3G networks are being shut down where I live (outside the US).
If I flash the Samsung U1 firmware and then change the CSC to my local region (with SamFW), will that allow IMS to register and thereby enable VoLTE?

Also, I ordered a B-stock carrier-unlocked S25 (I think originally Verizon). Will I run into the same IMS/VoLTE issue with a US carrier model, and would flashing U1 + CSC change fix it the same way? I'm sure plenty of people here where I live have US carrier-unlocked Androids, will they all run into the same issue?

(A little unrelated but is there a way to check battery cycle count which withstands a reset? I want to make sure the seller is telling the truth when he says it's not used besides for someone returning it within 14 days)

Thanks

 

[1075dn]

Update: I got VoLTE to work on my S8 without needing to flash or change CSC using the following trick!
Go to GitHub (can't post direct link, I get flagged for spam)
User: kyujin-cho
Repo: pixel-volte-patch
Issue: 136
Comment: 7th from top, user arsradu

Make sure to set APN type in all caps, and select the new APN

Do I have to do this every time I switch SIMs and get new APNs? If I flash the U1 firmware will it work by itself?
And will I have to do the same thing with my S25?

 

[VidJunky]

Welcome to Android Central forums. Glad you found an answer or at least a work around. I asked Google your question and got this reply.

Flashing the U1 firmware and changing the CSC using a tool like SamFW might enable VoLTE if your local carrier's settings are included in the U1 firmware's CSC list, and that CSC is properly activated. However, the trick you found is a software-based patch that manually forces the necessary APN settings to register IMS, a different approach that addresses the issue without a full firmware flash.

See the full response here.

I found this thread at XDA that might be helpful too. Read it here.