As stated by the title, the bootloader of the Xperia X8 (e15), X10 mini (e10) and X10 mini pro (u20) can unlock. A user on XDA Developers (The_Laser) release a tutorial on how to do, but for now there is no way to block it again.
What gives us an advantage unlocked bootloader?
The advantage is that we Flashar CUSTOM KERNELS, and forget about the limitations of our Xperia. We will have improvements to custom roms, WiFi and USB tethering native, remove the FPS limit, new Governors for the CPU, etc..
DISCLAIMER: This is a risky process, and can turn a smartphone into a brick. Nobody is responsible for the death of his phone.Also to unlock the bootloader, will void the warranty (for the moment to block the way back to the boot loader is not found) If you doubt your ability, do not risk it!
This tutorial is based on the experience of the Xperia X8.
Recommendations:
Its Xperia Drivers installed on your PC.
Disable the antivirus (I could find a "virus" in adb.exe eventhough it is not, and could even interfere with the process of unlocking the bootloader).
Having installed one of the most used ROMs: GingerDX V13 (preferably), and 2.0.7 v23b Froyobread MiniCM7.
Your phone will not have to be unlocked, or otherwise SETool2 be unlocked (unlock tool using credits).
Tutorial: (Translation and compilation of Russian and English language)
1 - You must have debugging enabled on the phone (settings -> applications -> Development -> USB debugging)
2 - Download the file (for Xperia X8 & W8, possibly X10 and X10 Mini Mini Pro).
DepositFiles.com
LetitBit.net
TurboBit.net
3 - Connect your phone to your computer on, and do not give any button to leave it as is (this comes from the USB debugging).
4 - Run the file msm7227_semc.exe:
If your phone is not unlocked, open the file msm7227_semc.exe (run it as administrator if you use Windows Vista or 7) and as stated there, press any key to continue and unlock the bootloader.
If your phone is unlocked but uses the other file SETool2 msm7227_setool2.exe and do the same.
5 - Wait a few minutes (maximum 5), while you can compare what goes on the black screen with what is in the log file [example_output.txt] that is in the same folder.
Code:
process requires standard 2.x android firmware.
Press any key to continue . . .
Getting ROOT rights.
1743 KB/s (585731 bytes in 0.328s)
error: protocol fault (no status)
Waiting ...
Removing NAND MPU restrictions via SEMC backdoor. Permanent. Require ROOT rights.
192 KB/s (3087 bytes in 0.015s)
success
Waiting ...
Getting ROOT rights.
Waiting ...
Writing patched semcboot. Two step process
First, we need get access to semcboot area
504 KB/s (8064 bytes in 0.015s)
Second, we need to write semcboot ;)
1130 KB/s (596916 bytes in 0.515s)
successfully wrote 0003ff00
Press any key to continue . . .
6 - Wait until it says press any key to continue (press any key to continue) and ready your bootloader is unlocked.
Credits: (XDA Forum) Blagus, the_laser, & co.