Unlock Bootloader Neo / Neo V

There is 2 ways to unlock your bootloader, Sony Official Way and Unofficial Way (Test Point Mode).

Make sure your device can be unlocked “Type: on Dialer: *#*#7378423#*#*
Bootloader Unlock Allowed : [Yes]

1. Sony Official Way

Sony has provided a website where we get an unlock code for each IMEI no. type in that code and your bootloader will get unlocked officially . This is the easiest unlocking method possible . Wait there's more , official unlocking method does more bad than good , like
1. will void warranty
2. Will loose DRM & track Id related stuff
3. No official phone updates via SEUS/PCC or OTA

If you don't care about them please go ahead and click this LINK and follow on-screen instructions on that site.
or
You can use Flashtool with Unlockbootloader plugin. You can download Flashtool in this website LINK

2. Unofficial Way (test point mode

This method overcomes all the three limitations , but you will need to do a little work manually , this method introduces us to a new word called Test Point (Of all those 8 golden points , only the point which is indicated by the arrow is the Test Point  .For NEO V test point is located deep within a slot covered by a black patch which is above our sim card slot (see this picture and remove the black covering) .

It is used for function-test during production. & we are going to ground that testpoint using a simple wire .instead of that pin you can use any conducting material (wire , safety pin , paper clip , but make sure its diameter is not more than that of the test point else it will touch other points and might brick your phone)

Ground : ground is refereed as the negative battery pin of the phone

STEPs :

Download & extract S1tool from this LINK

Run s1tool, press 'Patch semcboot' and follow instruction.

Using S1Tool

1. Click in IDENTIFY button. Connect your device in flashmode, turn off your device, press and hold "BACK Button". Information abbout yur device will appear. after that, unplug your device.
2. Connect test point to the ground and attach USB cable. Wait while Windows shows finding new device. Windows won't find appropriate drivers. select drivers manually from the archive of S1tool. Agree to install 'untrusted' drivers.
3. Click Patch SEMCBoot and follow instruction

Check these strings in Loader Version
If the strings begin with "R" big "R" then bootloader is LOCKED
If the strings begin with "r" small "r" then bootloader is UNLOCKED

RELOCK : : ONLY THE RESTORE BUTTON PRESENT IN S1TOOL WILL RELOCK YOUR BOOTLOADER , other procedures will not work.Connecting TP to ground while using RESTORE button is not necessary.

source : Xda and Google