SM-G892A Galaxy S8 Active Flash/Carrier Switch

Check this out first. https://www.reddit.com/r/GalaxyS8/comments/7jdcno/psa_with_the_latest_us_carrier_updates_your_phone/ That being said, S8 and S9 models ending in the letter "U" probably will work. Usually, this works when a phone is carrier unlocked and you switch sim cards. With these models you do not normally get a sim unlock screen. (if it is already unlocked) unlock through your carrier. S8 and S9 models have trouble with non verizon mvno sim cards. Trick - boot with a Verizon sim card (good or bad) ((The phone will switch settings to accommodate the verizon sim card. YOU SHOULD SEE A VERIZON SPLASH SCREEN AT START UP. Once up, verify the verizon access point is set. hold the power button down - choose emergency mode ---remove the verizon sim card, put in the non verizon CDMA card - hold the power button, turn off emergency mode and you verizon settings will be there. DO NOT RESTART THE PHONE. or you will have to go through it all again. Works on my S8+ G855U, maybe your ATT G892U. Note, the "U1" models are supposed to switch without the gymnastics with the sim card.

Just checked Sammobile. You may be out of luck. https://www.sammobile.com/firmwares/. Your model Sm-G892A has valid firmware for ATT and Sprint. Your firmware looks correct for an unknown XAS model. That being said, you could try the same tricks before with a Sprint sim card and a Sprint mvno card. Red Pocket carries all four carriers Get a non active sprint card on ebay. pennies. I started by going back to the original firmware. Then learned the upgrade process and took mine from 2017 stock 7 nougat up to 2020 9 Pie. Again, make sure you are unlocked from ATT first. If it doesn't switch on booting with a different sim card, I doubt you will have much luck.

---------- Post added at 09:42 PM ---------- Previous post was at 09:41 PM ----------

correction Sprint and T-Mobile.

---------- Post added at 09:48 PM ---------- Previous post was at 09:42 PM ----------

Last thing. I did notice if I used an ATT sim card in my S8+, it would boot to ATT Splash. If I used T-mobile, it would go to T Mobile Splash. However, if I did the trick while using an ATT card (i.e. emergency mode and switch the card To Red Pocket mvno for ATT gsm) it still worked. However, if I ever shut it down and restarted it would go to the T-Mobile splash even though I had the Red Pocket (ATT specific card) Therefore to get the ATT settings back, I would have to do the sim/emergency mode procedure again.

I have the SM-G892A, unlocked, and I'm using it on T-Mobile. APN all correct. Booted from stock with the TMO card but can't get the phone to display Wifi Calling option. This is the only reason I would try rooting and flashing TMO firmware. Which sounds sketchy from what I read above. My question: Any other thoughts on activating Wifi Calling? Thanks for responding.

Axilarry, you have a g892a on T-mobile? How did you do it? I can't get mine out of att 'mode', preconfig only gives me the att option. Custom rom, root? Please share.