bootloader and SIM unlock are two different things and people tend to confuse about it.
This phone is SIM unlocked out of box. ie, can be used with any GSM carriers around the world.
boot loader unlocking is done to root or install custom ROMs. A locked bootloader is always safe so most manufacturer keep it locked.
but unlocking bootloader for nexus devices is a piece of cake.
i have samsung galaxy music duos GT-S6012. can't figure out if my device's bootloader is locked or not, nor do i know as to how to CHECK even that. my problem is i want to root the device. somebody said i must unlock the bootloader. can't find any universal method of rooting the said device. this is my first android mobile device and i m a totally newbie to the android world. can anybody help me please ?
better to unlock it sooner if you think you will because it will wipe your device as a factory reset. You can tell if the bootloader is unloed when you boot up an unlocked icn will show under the word Google before the Nexus X logo.