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  UMTS
Step 9: Now select DEBUG SCREEN, followed by  PHONE CONTROL.
Step 10: From the next screen, pick  NETWORK LOCK.
Step 11: You’ll get three options. Hit the one that says  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 COMMON, and then  NV REBUILD.
Step 13: The phone will tell you that a Golden Backup exists. Tap  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