Samsung Galaxy S4 is available in both SIM locked (carrier locked) and SIM unlocked conditions for purchasing. While SIM unlocked S4 can be used anywhere without any restrictions, SIM locked version can only be used in specific countries and under specified networks. Here is how to unlock SIM locked Samsung Galaxy S4 GT-I9505 for using in any country and under any network.
Galaxy S4 provides users a way to carrier unlock (SIM unlock) their phone with few steps. It is fairly a simple process and requires no special tool. Just follow below steps to SIM unlock Galaxy S4 GT-I9505.
Warning: Though it looks like a simple process, unlocking your device is a risky job. Do it at your own risk. We’ll not take any responsibility for any loss caused by this method. In addition, this method is for Galaxy S4 GT-I9505 only.
1. Enter into Service Mode: Dial *#0011# and press Menu button (left soft key) and then tap Back key from the list.
Once gain press Menu key and select KEY INPUT. Enter 1 and press the OK button.
2. Enter into Service Mode main menu: Press Menu button and then tap Back key again.
In Service Mode main menu, tap  UMTS -> DEBUG SCREEN ->  PHONE CONTROL ->  NETWORK LOCK.
You will get three options. Tap the option  PERSO SHA256 OFF.
3. Go back to Service Mode main menu: Press Menu button and then Back key to return to main menu. In Main Menu, choose COMMON, and then  NV REBUILD.
Now, your phone will say that a Golden Backup exists. Just tap  Restore Back-up option.
4. Final: To complete the process requires few minutes, so be patient. After finishing the process your device will reboot automatically.
Once rebooted your Galaxy S4 is SIM unlocked (carrier or network unlocked) permanently. Enjoy!