Usually you expect a smartphone Galaxy S3 comes with unlocked bootloader, making it easy to upgrade or install unofficial ROMs (other than the Samsung). This isn't the case with Galaxy S3 of Verizon company.
The folks at XDA Developers know very well that this unit has locked the bootloader, although not impenetrable to "hack".
Verizon sent to various parts of the Korean company with the bootloader locked, but the company left open other variables. Thus, there have been comments about a possible break this blockade by RootzWiki.
Apparently the locks made by companies just leave more "fun" to search for "unlock" these blockages. Who appreciates the unlocks are users!