[AT&T Samsung Galaxy S 4 General] MajicDroidPirate:
I'm posting this simple guide compiled from various posts all over the internet on how to SIM unlock the gs4-i337 AFTER you installed the MF3 base-band ota. I have personally confirmed this works on the At&t GS4 I337 on MF3 baseband, I do not know about other variants I take no credit in any of this I am not a developer (yet) all credit goes to them, your welcome to thank me but if you do please thank them too. I will post all my sources at the bottom of this post

:D ALSO note to MODS,

If I happen to have posted this in the wrong section you may feel free to move it and I will not complain, I do not have many posts on XDA,

Step 1. ROOT the phone. How? Thanks to Jortex we can now root on MF3 update

Step1A. Insert a micro SD card into your computer, you may need a mini/micro adapter to fit it. use an sd card you have nothing on or move the files over to your computer because we will be formatting the card and you wil loose everything on it.

Step1B. (I only know how to do this on windows, you can research mac or linux) Go to computer (or my computer on older systems) right click and click format, have quick format selected and under file system click the down arrow and select exFAT (this is very IMPORTANT or it will not work)

Step 1C. download this file http://xdaforums.com/attachment.php?attachmentid=2165629&d=1375669716 (link copied from Jortex thread)

Step 1D Extract the file into the now exFAT formatted SD card, if you need an extractor I suggest 7-zip which was created by a non-xda devoloper but one that still deserves mad props Igor Pavlov you can grab his program at http://www.7-zip.org/

Step1E. Download Android Terminal Emulator from the play store to your device here is a quick link

https://play.google.com/store/apps/details?id=jackpal.androidterm&hl=en and I would tell you to thank Jack Palevich however I dont think he has an xda account either (I could be wrong) regardless go and give him 5 stars on the market for this great terminal

Step 1F. Pop your exFAT SD with the root files into your phone and open android terminal

Step1G. Type the following into the terminal exactly, PRESS ENTER AFTER EACH LINE, ITS CASE SENSITIVE ITS SPACE SENSITIVE DONT FORGET PERIODS IT MUST BE EXACT AFTER EACH LINE PRESS ENTER DO NOT SAY IT DIDN'T WORK IF YOU TYPED THE COMMAND WRONG

cd /mnt/extSdCard

./pwn

./script.sh

I know im stating obvious here but youd be surprised how many people can get this wrong so

after cd there is a space this is the only space

the S and the C in SdCard are capital nothing else is capital

there is a period in ./pwn

there is also a period before ./script.sh

Thats it, if your rooted you'll notice that your $ in terminal emulater has changed to a #, reboot the device go and update SUPERSU and go thank chainfire for making SUPERSU and the next app im about to discus too!

Congrats now your rooted on MF3, but your still locked, well your in luck thanks to the greatest XDA DEV in my opinion (sorry devs but this guy has made my android life so much easier then anyone else your all really good hardworking devs, but this guy is amazing) yes I'm talking about the one and only chainfire, the devoloper of apps like SuperSU TriangleAway, CF-AutoRoot and about a dozen other amazing apps has now created an app made called [root] RegionLock Away which you can eaither "buy him half a beer" and purchase it at the playstore here https://play.google.com/store/apps/details?id=eu.chainfire.regionlockaway&hl=en or he also offers it free on his xda post (link coppied from xda) http://xdaforums.com/attachment.php?attachmentid=2370437&d=1383564029 Chainfire thought he made a region unlock app for the note 3, and while that may be true apparently its also a sim-unlock for the galaxy s4, there is already a post here on xda saying this app works but they seemed to have failed to mention that the phone must be rooted and how to root it, regardless you can still go thank egolabbakhsh for testing this on his device and giving me the confidence to try it, I also would like to thank tanvir islam because it was actully his comment on the app that said it unlocked his S4 that made me look in this direction, I'm not going to post a link to his google+ page because I don't know if he wants 10million people thanking him or not but regardless I thought I'd mention his name And most of all I would Like to thank Josh as being the man who let me test and confirm this method on his phone, not sure what his XDA handle is but I'll update this when I find out.

Okay now that Is all out of the way the rest is super easy

Open RegionLock Away

Grant SuperUser Permission

Press Region Unlock

YOURR DONE!!! CONGRATS!!! it works...set up your new sims apn to get internet+mms and your golden:good:

Now here are all the original XDA POSTS

First Jortex for root method

http://xdaforums.com/showthread.php?t=2387577

Next ChainFire for RegionLock Away

http://xdaforums.com/showthread.php?t=2470551

And Finally

egolabbakhsh for testing this app

http://xdaforums.com/showthread.php?t=2514607

GO AND THANK THEM ALL AND IF YOU HAVE TIME LEFT THANK ME TOO!!!;)