[Sprint Samsung Galaxy S 4 General] chris41g:
There seems to be some confusion on the matter here in the forums.

Can I sim unlock my Sprint Galaxy S4 to use ATT/TMobile sims?

Yes

Can I do it using a Lollipop Rom?

Yes

Can I do it once I flash a KNOX bootloader?

Yes

Can I do it on OD2?

I don't think so, but maybe... The best bet is to use NG2 and then experiment from there...

Can I do it without reading/paying attention/following directions?

No.. but if you made it here, you're doing OK so far...

First off, there are 2 kinds of SIM unlock for the SPH-L720. International unlock, and domestic unlock. We will cover both.

To unlock for international carriers SIMs, you have a couple of options.

a. Have sprint unlock it for you

b. Do it yourself.

I prefer b, almost always.

Lets start off with what you'll need:

Drivers for the phone, I'm too lazy to find those, but if you can't, you are way out of your depth here.

SSU.apk from here.

An NG2 Stock Rom (modem and ROM) here is an Odin tar that i used when I did it.

Odin from the same post that tar came from... (here)

TWRP recovery in tar format from here (i used 2.8.4.0, but I don't think that matters)

adb ( i use this minimal adb installer but any adb install will work.)

THIS WILL PROBABLY WIPE ALL YOUR DATA.

Put your phone in Download mode (Power + Vol Down)

Open Odin

Click the PDA button, choose the tar.md5 file you're flashing. (the stock ROM from earlier)

Uncheck Auto Reboot

Plug in a decent USB cable, from the phone to the PC

Hit start

It will take a few minutes, no worries unless you get an error.

When it is done, Hold Power + Vol Down until the phone reboots into download mode again

Click PDA in Odin and load the TWRP tar you downloaded earlier.

Hit start. This will take significantly less time.

When it is finished, Hold Power + Vol Up to reboot into recovery.

When TWRP is fully loaded, click reboot then reboot system.

It will tell you that the ROM is not rooted, and ask if you want to do that. (if you used the tar from above) and of course we want to, so let it.

Let the phone fully boot up.

Goto Settings, More, About Phone.

Find the line that says Build Number, click that line a bunch of times until it says "You are now a developer".

Now hit back, and goto Developer Settings.

Find Debugging mode and enable it.

Using adb

adb devices

that will respond with whether it finds your device or not.

adb install /path/to/SSU.apk

that will install SSU.apk from earlier..

You'll want to have the screen of your phone on for this part because you will need to approve your PC to connect.

Goto your app drawer, and run SSU

Click the Unlock button

Now your phone is SIM unlocked for international carriers... But what if you want domestic carriers too?

Unlocking for Domestic Carriers

First things first, you have to do the International Unlock explained above (you didnt think you were gonna get out of that did you?)

After that, load ADB back up

adb shell

su
am broadcast -a android.provider.Telephony.SECRET_CODE -d android_secret_code://27663368378

That will pop up a menu on your phone

Click (UMTS) then (DEBUG SCREEN) then (PHONE CONTROL) then (NETWORK CONTROL) then (GCF) then the top option.

Now reboot.

You are now unlocked Internationally and Domestically. Goto your mobile network settings and put your apn settings in (if they arent already there off the sim) and you should have data too.

From here you have a couple of choices.

a. Stay on NG2

b. Goto another ROM (i usually just flash CM at this point, YMMV)

c. experiment yourself and try to use OD2 (I've heard flashing the OD2 modem relocks it, didnt try because I didn't want OD2)

If you stay on NG2 then I suggest this apk to Stop the Sprint Hands Free Activation from nagging the **** out of you..

NOTE: as of tonight, any CM12.1 nightly after 6/23 causes a No Sim card error. This has nothing to do with the unlock, its just messed up, so until its fixed use the 6/23 nightly.

Hopefully that answers some of the questions I keep getting in PMs and what not.. If you have any question, feel free to ask.

I might not answer them, because I rarely frequent the forums anymore, but lots of people here can probably answer the questions you have.

Thanks to [MENTION=2684188]autoprime[/MENTION] he's the one that found the original unlock for this phone, and tons of others.

Thanks to [MENTION=3266146]random45[/MENTION] for posting the ROM i used

Thanks to [MENTION=3558630]shimp208[/MENTION] for posting (making?) the minimal adb install that i use

Thanks to [MENTION=3456671]Sloosh[/MENTION] for making the Hands free activation disabler apk

Thanks to [MENTION=912474]Dees_Troy[/MENTION] for TWRP and just being cool in general

Thanks to [MENTION=307784]aalyatim[/MENTION] for the SSU.apk

Thanks to cyanogen and Team CyanogenMOD for all they do..

Thanks to [MENTION=5592476]imaxuout[/MENTION] for keeping this topic alive in a few threads

Thanks to [MENTION=2555414]AndroidKing[/MENTION] for a similar thread.

Thanks to nicotheandroidguy also.

And anyone else I forgot (I'm sure I did)