Out of the four major American carriers, Verizon was the only one who required a locked bootloader on its version of the Samsung Galaxy S III. Naturally, this upset many developers and Android enthusiasts who enjoy flashing custom ROMs. As many expected, however, it would be only a matter of time before deft developers would be able to create a method to unlock the bootloader. That day has come.
According to an XDA-Developers post by AdamOutler, an unsecure bootloader can be installed onto the Verizon Galaxy S III leaving you open to flash custom ROMs through Odin. Getting access to the bootloader and unlocking it is the first major step in flashing custom ROMs and this is a great feat by devs.
In order to unlock the bootloader on your GS3, you will have to follow the instructions in the link below and apply it running Mac OS X or Linux.
As always, proceed at your own discretion, attempting to unlock the bootloader will void your warranty and could brick your device if done improperly. Also, AdamOutler mentions several times to never accept a Verizon official software update after unlocking the bootloader as it will brick your device.
I guess there’s no need for that Developer Edition Galaxy S III on Verizon Wireless — thanks anyway Samsung.