How to Unlock Sony Ericsson Xperia Bootloader

1. Download fastboot package from here and x86/x64 drivers from here.
2. Head over to Ericsson website.
3. Scroll to the bottom of the page and click ‘Continue’ button.
4. A pop-up window will appear. Click ‘Yes, I’m sure’. And then click ‘Accept’.
5. Enter your name, email address and the first 14 digits of your phone’s IMEI number. (IMEI number can be checked by dialing *#06# on your phone).
6. You will see now unique boot loader unlock key. Write down the key on a notepad so that it can be used in future.
7. Extract the fastboot package and open fastboot folder.
8. Hold SHIFT and right-click on the background of the folder.
9. Select ‘Open command window here’ as shown in below image:

10. Hold the unlock button (for Xperia Neo/Arc/Pro, hold Menu button and for Xperia Play, hold Search button) on your phone and connect it to your computer via USB cable.
11. In the command window, enter fastboot.exe -i 0x0fce getvar version
12. If you get a value in return, it means your have correctly connected your phone.
13. Enter fastboot.exe -i 0x0fce oem unlock 0xKEY (Make sure to replace KEY with the unique key that you noted in the notepad in Step 6).
14. You will have Bootloader Unlocked your device now.
Please note that as per some users who tried above method, the process works well in 32 bit Operating System like Windows Vista / Windows 7 but stucks in Windows 7 64 bit.
Let us know how it went for you.