As all the other manufacturers (minus a few such as LG) are headed down the locked up and signed bootloader trail, Sony Ericsson is headed in its own direction. Today their Bootloader Unlock site went live with the full instructions on how to unlock the pesky bootloader on the Xperia Arc, Xperia Play, Xperia Neo and Xperia Pro (all 2011-onwards devices). There’s over 14 steps to the process, which if you’re a dev, isn’t that many at all, and it’s fairly straightforward. Just grab your IMEI, download the Android SDK and a few other SE files and sign your life away. So yeah, your move HTC, Motorola & Samsung. Hit the source link to get your dev on.
Source: Sony Ericsson - Unlocking the boot loader.