Unlocking bootloader on Xperia 2011 devices
Introduction and prerequisites
With this method you wont need to download the android SDK and instead can download a small package of files that have been uploaded below, this saves around 1-2GB of bandwidth.
ADB and Fastboot Package - http://db.tt/B5vG1ynM
Firstly we should confirm your phone can be unlocked.
To check if your phone can be rooted go to the phone dialer and tap *#*#7378423#*#*.
A service menu should pop up.
Tap Service info > Configuration > Rooting Status.
If it says boot loader unlock allowed then you are good to go.
if it says not allowed or no then you will need to pay to have the boot loader unlocked via unlock-bootloader.com.
Now we need to get your IMEI to do this type in the dialer *#06# another window will appear with your IMEI number write this down somewhere as you will need it later, alternatively you can get the IMEI from under the battery.
Retrieving your IMEI number
Now we can begin. Turn of your phone. Hold the search button while plugging in the usb lead (LED lights up blue).
Your computer should prompt you to install drivers for the new device if it does then select 'install manually' and browse to the location of the drivers, depending on your system architecture (X86 or X64) select the appropriate folder it should then install the drivers if you get any prompts about unsinged driver just install any way. if something doesn't happen like it is suppose to try going to device manager.
Next we need to go to sony ericsson's bootloader unlock site read through to confirm you understand what your doing then click continue.
OK now check both boxes and press "i accept".
Now we need to fill in these fields (IMEI is the number you wrote down earlier if it doesn't work remove the last number and try again)
Press submit and you will see your unlock key copy it for later.
Finally after installing the drivers we need to run the software called fastboot now to make it easier for you guys i have included a simple bat file which will load CMD at the correct location.
So load run_me.bat and make sure the BLUE LED on your phone is still on. if it is then type this in to the new cmd window. if it isn't then repeat the usb and search button procedure.
fastboot.exe -i 0x0fce oem unlock 0xKEY
replacing KEY with your key. for example.
fastboot.exe -i 0x0fce oem unlock 0x726802F75671552D
Your phone should now be unlocked.