[T-Mobile Samsung Galaxy S 4] jmacguire:
I read this thread many times over before unlocking my T-Mobile M919 and Metro M919N Galaxy S4 smartphones. http://xdaforums.com/showthread.php?t=2283068

Both phones were on Android 4.4.4 when I got them and the newer, revised method linked above near the end of the thread scared the crap out of me with its "ERASE EFS 1/2/3."

The original method would no longer be possible as most people's phones are updated past the OP's firmware version and the 4.4.4 bootloaders can not be downgraded past 4.4.2. I unlocked both of my phones by doing the following.

1) downgraded both to T-Mobile 4.4.2 firmware TMB-M919UVUFNB4-20140314115123-v4.4.2 Both phones can run either Metro or T-Mobile firmware. I rooted both phones.

2) downgraded the modems to MDL and shutdown the phones.

3) ran Region Lockaway and rebooted.

4) Used the original steps in the thread linked above.

Here they are with a tweak or two

"Goto phone dailer, and enter *#27663368378# for the debug service menu. ( I used the *#0011# dialing method, chose "key input" with the left menu key and then entered 1 and ok and waited 15 seconds. You can also use the "PhoneINFO Samsung" app on the PlayStore if you root your phone before accessing the service menu)

In "ServiceMode", select [1] UMTS

In "UMTS MAIN MENU", select [1] DEBUG SCREEN

In "DEBUG SCREEN", select [6] PHONE CONTROL

In "PHONE CONTROL", select [6] NETWORK LOCK

In "NETWORK LOCK", select [3] PERSO SHA256 OFF

It should show:

SHA256_ENABLED_FLAG[1]

SHA256_OFF => SHA256_ON

Now touch the first line SHA256_ENABLED_FLAG[1]

It should show:

MENU NOT EXIST

PRESS BACK KEY

Current Command is 116631

Now press the menu button and select "Back"

It should show:

SHA256_ENABLED_FLAG[0]

SHA256_OFF => Not Change

Again, press the menu button and select "Back", and you're back in the "NETWORK LOCK" screen

Press the menu button and select "Back", and you're in the "PHONE CONTROL" screen

Press the menu button and select "Back", and you're in the "DEBUG SCREEN" screen

Finally, press the menu button and select "Back", and you're back in the "UMTS MAIN MENU" screen

Select [6] COMMON

In "COMMON" screen, select [6] NV REBUILD

Now you are in the "NV REBUILD" screen, you should see the following text:

------------------------------

Golden-Backup exist

You can Restore Cal/NV

------------------------------

Now for the final step.

In "NV REBUILD" screen, select [4] Restore Back-up

The button lights for menu and back should come on, and the phone will auto reboot in a few seconds."

After rebooting, I ran Region Lock Away again and shut down. I inserted AT&T sim cards in both phones. I cold booted both. Upon reaching the home screens, I immediately saw AT&T in the top left corner and 4G to the right with five bars of signal strength.

I upgraded both phones back to their 4.4.4 firmwares, rooted them again, and ran Region Lock Away again. (Remember, Region Lock Away says that it is writing to the modem)

Both phones were still domestically unlocked and worked perfectly.

Why downgrade the firmware to 4.4.2? When I downgraded just modems and not the 4.4.4 firmware, the phones were sluggish and the service menu would crash or the phone would simply not respond to anything. Downgrading the modem firmware to an earlier version than the 4.4.2's NB4 modem worked perfectly.

There may be other ways to do this, but my method is much less risky that the newer method posted in the thread I referred to. Is the Region Lock Away necessary so many times? I can not be certain, but my method worked PERFECTLY on two phones side by side. I would not erase my EFS info regardless of if I had a backup or not.

Good Luck.........