[Sony Ericsson Xperia Mini, Mini Pro, Xperia Pro, A] illus4:
As some ones of you including me still have not unlocked the bootloader at unlockbootloader.sonyericsson.com simply because not willing to lose the functionality of DRM and the TrackID, here comes another solution.

***WARNING***

The following operations may harm your device and your warranty may be void.

Neither I nor any other forum members mentioned below will be responsible for any of your loss.

Continue reading at your own risk!

***WARNING***

[requirements]

A 2011 Sony Ericsson XPERIA device with a still looked bootloader (this should work on all the 2011 XPERIA models but I have only tested on an XPERIA ray)

[referencing links]

Reading all the links below before conducting any operation is strongly recommended.

http://xdaforums.com/showpost.php?p=18013064&postcount=44

http://xdaforums.com/showpost.php?p=18038659&postcount=54

SETool Test Point Cable For Arc - Neo - Play

unlock st18i ryay

sk17 testpoint and request for help.

[unlocking your bootloader]

Find the test point of your device (see the referencing links, you may have to register an ID at support.setool.net to view some of the attachments)

Download s1tool from this thread and extract the 7z file

Turn off your phone

Connect the USB cable shield and the test point with a paperclip or some other wire

Attach the USB cable to your PC, when Windows finds a new device, disconnect the test point and manually install the driver contained in the s1tool.7z archive

Run s1tool.exe, click “Patch SEMCBoot” then follow the instructions on the screen and your bootloader will be unlocked

After the bootloader is unlocked, you can flash custom kernels or do something else like rooting your phone etc.

I am using an XPERIA ray* and I have unlocked my bootloader then rooted it. The TrackID works and no side effects found yet. Currently I have no idea about how to relock the bootloader so do this at your own risk.

Below is my s1tool log:

01/10/2011 22:36:09 Welcome to S1 tool.
01/10/2011 22:36:09 That is small and crippled subset of SETOOL2 service tool.
01/10/2011 22:36:12
01/10/2011 22:36:12 DETACH USB CABLE FROM PHONE
01/10/2011 22:36:12 REMOVE BATTERY FROM PHONE
01/10/2011 22:36:12 ATTACH TESTPOINT
01/10/2011 22:36:12 PRESS "READY", THEN ATTACH USB CABLE TO PHONE
01/10/2011 22:36:12
01/10/2011 22:36:50 PROCESSING ...
01/10/2011 22:36:51 REMOVE TESTPOINT NOW, THEN PRESS "READY"
01/10/2011 22:36:51
01/10/2011 22:36:56
01/10/2011 22:36:56 TO CONNECT NEXT PHONES
01/10/2011 22:36:56 X10 Xperia,E10 Mini,E15 Xperia X8,U20 Mini Pro
01/10/2011 22:36:56 LT15 Xperia ARC,MT15 Xperia NEO,R800 Xperia PLAY
01/10/2011 22:36:56 PRESS AND HOLD "BACK" BUTTON...
01/10/2011 22:36:56
01/10/2011 22:36:56 ST18 Xperia RAY,ST15 Xperia Mini,SK17 Xperia Mini Pro
01/10/2011 22:36:56 PRESS AND HOLD "Volume Down" BUTTON...
01/10/2011 22:36:56
01/10/2011 22:36:56 PLEASE ATTACH TURNED OFF PHONE NOW
01/10/2011 22:36:56
01/10/2011 22:36:57
01/10/2011 22:36:57 RUNNING S1_LOADER VER "R4A062"
01/10/2011 22:36:57 LOADER AID: 0001
01/10/2011 22:36:58 FLASH ID: "0098/00B3"
01/10/2011 22:36:58 LOADER VERSION: "r4A069"
01/10/2011 22:36:58
01/10/2011 22:36:58
01/10/2011 22:36:59 SEMC SIMLOCK CERTIFICATE, PROCEEDING
01/10/2011 22:36:59 FINISHED
01/10/2011 22:36:59 Elapsed:46 secs.

(*Updated 10 Dec 2011: According to the replies below, this method may not work on branded phones.)