Only certain releases of four Sony Ericsson devices are eligible for a boot loader unlock right now, namely the Xperia PLAY, arc, pro, and the neo. However, it is quite possible for upcoming smartphones to join the list of modder-friendly handsets. In a nutshell, the unlocking procedure goes like this: you provide SE with your name, email address, and the smartphone's IMEI number, after which you will be able to download all the software needed for the boot loader unlock to be performed.
Of course, Sony Ericsson does not forget to warn you that a ton of things can go wrong. Unlocking the boot loader may have unwanted side effects like ending up with a bricked device or voiding its warranty. If you choose to proceed anyway, we urge you to be very careful, and do not forget to share your modding endeavors with us by leaving a comment below.
source: Sony Ericsson via Electricpig