How to unlock and install Android 4.4/5.1 Lollipop into Xperia U ST25i (Working bootloader unlocking method) Tutorial

Hello again guys and welcome to this new Android devices tutorial, today I hardy want to share this tutorial with everyone owning an xperia smartphone and specially for Xperia U users, Sony Xperia devices are considered as the most tricky devices to root, unlock and install costume ROMs, and so I want to share with you a "Real" tutorial to help users unlock boot loaders and install latest custom ROM such as CM11 or CM12 into their Xperia U.

First thing first do this at your own risk, also it might void Sony's waranty.

What you need:

Computer and USB cable.
Your Xperia U ST25i charged up to 75%.
Download the Fastboot tool including driver from Here.
Download this Xperia U driver (in-case you need it) from HERE.
Download Flash too from HERE.
Check the debug option in dev menu and unknown sources in security.

First thing first let's check and unlock the boot-loader.

Unlocking the bootloader for Xperia U:

First lets check if your bootloader is unlocked:

Open the dialler and enter *#*#7378423#*#* to access the service menu, tap Service info > Configuration > Rooting Status. If Bootloader unlock allowed says Yes, then continue.

Now go to Sony official unlocking page HERE.
Here is the trick now, in the official page "Xperia U" is no listed on scroll menu, you can Select Xperia S instead, many users try it and work, I personally try it and the key work fine.
next confirm and enter your email then follow the process.
PLEASE note down your imei code into a safe place.
After you get the unlock key note it down on a safe place txt file.
Now connect your phone in fastboot mode (power down xperia the press vol-up and connect the usb cable).
It's important to check drivers installed.
Then go Fastboot zip, extract then go to fastboot folder and press shift+right click and select command prompt.
Type this in the CMD window "fastboot.exe -i 0x0fce getvar version".
You shoult get '0.5' value.
If yes now type "fastboot.exe -i 0x0fce oem unlock 0xKEY" AND Whange the key with the Key you get from Sony.
After pressing Enter, your device bootloader must be unlocked.

If you still unable to get the steps just watch the bellow video it meight help:

Installing CM11 Android 4.4 Custom ROM and Recovery:

Download The ROM from Here and the Gapp from HERE.
And if you want to install Android 5.1 Lollipop CM12 ROM download it from HERE and GAPP from Here, (Please not that on this date '02/06/15' CM12 have some problems now like video recording).
Now run flashtool, install drivers, and click on flash icon->fastboot mode, select Reboot to fastbootmode (adb or fastboot).
Then select kernel to flash and select the boot.img from the CM.zip file.
If you get assert failed on xperia u when installing the CM ROM, then your Bootloader is still locked, you need to unlock it !
That's it now you can boot to the recovery (Power down, then power the phone when the Sony logo appear press repeatedly on Vol-Down).
Now go to install and select the CM ROM zip file then the Gapp zip file, then wipe data+cache+dalvik.