I tried this on my "UNROOTED" Samsung Galaxy S4 GT-I9505 with an MGA based firmware and it works perfectly.
Simple lang po pag unlock ng network ng s4 natin you just need to follow carefully the steps provided below and a bit knowledge on how to flash your phone via Odin.
I dont know if this works on other variations of S4 too. So please do it at your own risk.
1. Odin v1.85 or later (http://forum.xda-developers.com/showthread.php?t=2189539) credits to daerragh xda for this
2. XXUAME2 modem (http://d-h.st/IFe) credits to DjeMBeY of xda for this
3. Unaccepted SIM card
NOTE: if youre already on ME2 baseband di na po kelangan ng Odin at ME2 na files just proceed to PART II of this TUT.
PART I (for phones with baseband later than ME2)
1. Flash the downloaded modem provided above through Odin v. 1.85 or later, be sure to browse it and load it into PHONE, NOT CSC or BOOTLOADER or PDA.
2. After flashing you now have an ME2 baseband. To check this please see your settings > More > About device and check the baseband version (I9505XXUAME2)
Please proceed to PART II if you already have the ME2 baseband if not please check your Odin version if it lies within the version I provided above.
1. Dial *#0011# on your phone and this will give you the service menu.2. Press the Menu key then Select BACK.
3. Press the Menu key again then tap KEY INPUT then enter 1 and press OK. (wait for 3-5 seconds)
4. Press MENU then select BACK.
" You are now in the SERVICE MODE MAIN MENU"
5. Select UMTS (you are now in the UMTS MAIN MENU) > DEBUG SCREEN > PHONE CONTROL > [NETWORK LOCK] > PERSO SHA256 OFF
6. Go back to the UMTS MAIN MENU by pressing Menu then select BACK
7. Select COMMON > NV REBUILD > RESTORE BACK UP
the device will freeze, black screen, Blue LED Lights, Menu and Back key ON. Wait for it to reboot (about a minute).
BOOOOOOM!!!! youre phone now explodes, just kidding. It is now SIM unlocked.
8. Turn OFF phone and put the UNACCEPTED SIM card (which is now ACCEPTED). :)
Hope this helps to everyone of you out there asking on how to unlock their phones for FREE.
This is a Permanent Unlock I dont think you can Undo the procedure if its already done. For those who are on postpaid, and if you are worried about your warranty being void...SIMPLE...do not unlock your phone hehe. Once again "DO IT AT YOUR OWN RISK" I am not responsible if your device will be broken, bricked or whatsoever.