This will require use of odin so warranty may be deemed void by samsung
IMPORTANT NOTE GOTO Setting>About Phone and note the firmware
Step 1: Download and extract these files
i9505-Unlock.zip
Step 2: Run odin and click
PDA and select
I9505-Unlock-4.2.2.tar
Step 3: power off your phone and disconnect it from the cable then
press volume down + home + power same time
Step 4: Connect Phone with pc and you can see a yellow color bar with COM listed.
Step 5: Press
start and wait for phone to restart.
Step 6: Launch the Phone app on your Galaxy S4, and dial in:
*#0011#
Step 7: Press the
Menu button followed by the
Back key. Then, hit the
Menu button again and
select KEY INPUT. Enter
1 and press the
OK button to enter ServiceMode.
Step 8: Press
Menu one more time and tap
back again. This will pull up the Main Menu for ServiceMode. Tap
[1] UMTS
Step 9: Now select
[1]DEBUG SCREEN, followed by
[6] PHONE CONTROL.
Step 10: From the next screen, pick
[6] NETWORK LOCK.
Step 11: You’ll get three options. Hit the one that says [3] PERSO SHA256 OFF.
Step 12: Now, you need to get back to Main Menu. To do this, hit the
Menu button followed by the
Back key. In
Main Menu, now pick
[6]COMMON, and then
[6] NV REBUILD.
Step 13: The phone will tell you that a Golden Backup exists.
Tap [4] Restore Back-up.
Now switch off phone insert sim and check if it doesn't ask for code on start hurray 80% work is over
Now Goto
http://forum.xda-developers.com/showthread.php?t=2192025 and Select the appropriate odin flashable modem for your S4 model and Firmware version.
Again use Odin to flash the new modem back to phone.
Now you have network unlocked S4 enjoy it with any carrier you want