[Sony Xperia S, Acro S, Ion] DooMLoRD:
Quick tutorial for unlocking & relocking the bootloader of the Xperia S/P/U/Sola.

this is the official way to unlock bootloader

Warning!

This procedure will wipe the /data partition of your phone, so you will loose all ur stored data, settings. SDCARD will NOT BE WIPED!!!

DRM keys WILL be lost forever

why to unlock bootloader?

u can flash custom ROMs/Kernels

u dont need to worry if the new firmware can be rooted or not as with unlocked bootloader u can always ROOT ur device

SE/Sony gives sneak-peaks/preview builds of latest OS which requires unlocked bootloaders, as they did with Xperia 2011 line (they had ICS alpha/beta), so who knows may be SE/Sony may give early builds of ICS (JellyBean???) ;)

Most of this is taken from lollylost100's his tutorial from ARC thread (all credits for that concise tutorial go to him, i have elaborated on a few things and added device specific changes)

btw i dont have this device, most of this testing was done on user darkpisces's phone so thanks a lot to him for helping me out!!!

[ before we begin unlocking bootloader ]

get the IMEI code for ur device: type *#06# in phone dialer to find it out, note only the digits (no dashes)

download the fastboot package

download the latest FlashTool Xperia Driver Pack and install fastboot drivers (common) & adb drivers for this device from the list!

make sure u have a windows PC with USB cable to connect the phone

power down ur phone and keeping the Volume Up button pressed connect the USB cable to PC this will trigger FASTBOOT mode and windows will start driver installation, which should be automatically done

once drivers are installed just disconnect cable and power on device

[ how to unlock ] (official way)

Go to: http://unlockbootloader.sonymobile.com/ and read everything!

At the bottom click 'Start Unlocking the Bootloader'

after u have verified that u can unlock bootloader, scroll to the bottom of the page and click "Continue"

you will get "are u sure prompt" accept it by clicking "yes i am sure" (i assume that u have read an understood it)

then accept the "legal terms"

finally u will get a "Create Unlock request" page, enter your IMEI (sometimes the last digit needs to be removed for this to work), name and email address

You should now receive your unique unlock key, its displayed on screen, SAVE THIS KEY SAFELY

Extract fastboot_with_Android_USB_file.rar and open fastboot folder

Hold SHIFT and right click on the background of the folder

Select 'Open command window here'

Connect your phone in fastboot mode (turn phone off, hold Volume UP button and plug in USB Cable) [make sure drivers are installed as explained above)

In the cmd windows type in fastboot.exe -i 0x0fce getvar version

If a value is returned (it will return 0.5), it means the phone is correctly connected

Type in fastboot.exe -i 0x0fce oem unlock 0xKEY and replace KEY with the key which u received earlier.

You're device should now be bootloader unlocked

If this tutorial is too much for you then itskapil wrote a step-by-step guide (and recorded a video also):

-Instructions: http://www.theandroidsoul.com/how-to-unlock-bootloader-xperia-arc-play-neo-pro/

-Video: http://www.youtube.com/watch?v=LRH3pC7MhEA

(the above videos and some steps are for Xperia 2011 devices, but most the steps are same for Xperia S/P/U/Sola)

Info on Relocking bootloader is in next post