Verizon's version of Samsung Galaxy S III comes with locked bootloader
However, if this is the doing of the nation's largest carrier, they have not stymied the hacker community. Rootzwiki says that it already has a workaround. You can head to the sourcelink for the directions. But be forewarned. You could end up accidentally bricking your brand new Samsung Galaxy S III and end up losing your warranty. Make sure you know what you're doing.
source: Rootzwiki, XdaDevelopersForum