3rd Alternative Method.
This 3rd alternative method is mostly only reported to be working for the Galaxy S4, however if neither of the other alternative methods have worked for you you can try this one as well.
Remove the simcard from the phone and then start the phone.
a. Go to the Dial pad and dial *#0011# b. Please click your MENU button (Bottom LEFT button) and click BACK on the menu that appears, Nothing will happen do not worry please move to the next step c. Please click your MENU button AGAIN and this time click KEY INPUTd. When the Key input box appears please input the number "1" and hit OKe. You will see a number 1 for a while, please wait until it changes into the SERVICE MENU f. Please click  UMTS >  DEBUGGING SCREEN >  Phone Control >  Network LOCKg. You will see 3 OPTIONS within Network LOCKh. Please click on number  Perso Sha256 INFO, the screen will change slightly i. Please hit the MENU button then when the menu pops up please carefully hit BACK to return to the previous screen j. Next Please click on number  Perso Sha256 ON, the screen will change again to a one line message k. Restart the phone on the screen by holding the power button and click RESTART l. When the phone prompts for the unlock code simply enter the unlock code provided to you m. Your phone is now permanently unlocked!
In case one of the codes mentioned above did not work and / or menu items are missing on your model please move on to the next alternative method as mentioned here
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