UPDATE: We’ve posted our own step-by-step simple guide for unlocking boot loader on all the Xperia phones released in 2011. You can visit the link here — Simple Guide To Unlock Boot Loader On Your Xperia Arc, Play, Neo and Pro
It sounds a bit strange but Sony Ericsson has come up with a detailed instructions set to unlock the bootloader of its flagship device, Xperia Arc. Those interested can head right onto this page (link here) to say hello to risks and then proceed to step-by-step guide. As for the risks, this will void the warranty of your phone and certain functions of your phone may not work. In the worst case, you may brick your phone (even after following SE’s instruction set to the letter) but we know it, many enthusiastic won’t stop at nothing — more so once root, custom ROMs and other hack-ish starts becoming available.
BTW, not only the Arc, but SE’s all phones in 2011 can have their bootloader unlocked by following the guide. Phones currently supported are — Xperia™ arc, Xperia™ neo, Xperia™ pro and Xperia™ PLAY.
Unlocking the bootloader will make it easier for developers to gain root access on the device and I think will help a lot thereby in the development of custom ROMs and custom kernels and stuff.
Via SE Blog