Did you see the "ROOT" in the title? This means that:
THIS APPLICATION REQUIRES ROOT.

Easily unlock your ROOTED T-Mobile/Wind Samsung Galaxy S 4G (Released in 2011)

Features:
* One button lock/unlock
* Backup/Restore
* Get your unlock code to unlock by hand
* Fragments Interface

Compatible phones (Must be ROOTED)
SGH-T959V (T-Mobile Galaxy S 4G)
SGH-T959W (Wind Galaxy S 4G)

Explanation of permissions:
WRITE_EXTERNAL_STORAGE
The app writes your unlock code (/sdcard/unlock_code.txt) and backups (/sdcard/efs_backup.tar) to the SD card

ACCESS_SUPERUSER
This is a root app

CHECK_LICENSE
Makes sure you're the owner of the app