[Part 2 - Profesional Way to Unlock & Root] - Unlocking the Bootloader

[Source: Lowyat.net Forum]

***NOTE***This may perform a factory reset on your device. You will lose all your APPS & DATA. Even the data on your SD Card! I'd recommend making a Backup to your computer BEFORE performing this.

Get the drivers
Uninstall any previously attempted drivers if they don't work and move to the next.
Option One: Steps 16-27.
Option Two: Try this one as well. Use CyanogenMod's Guide for installing ADB - Steps 16 through 27 replacing the file/location with the naked drivers.
PDAnet's drivers may work if the above options don't. Simply install PDAnet (after uninstalling any previous attempted driver installations) to get the drivers.

While that is downloading, on your Nexus 4: turn USB debugging on.
To do so; you must first go to Settings > About > Build Number and click seven times.
The actual setting can then be found in Settings > Developer Options > USB Debugging

Once the drivers are installed, navigate to the C:\android-sdk-windows\platform-tools folder on your computer.
Hold shift and right click. Select "Open Command Window Here."
On your phone: turn USB Debugging On. To do so; you must first go to Settings > About > Build Number and click seven times.
The actual setting can then be found in Settings > Developer Options > USB Debugging
Plug your phone into the computer. Now in this command window type:

CODE

adb reboot bootloader (Hit Enter)
Your phone should now boot into a screen with a green android with his chest exposed.
Type this:
fastboot oem unlock (Hit Enter) 

If your Command Prompt displays the message "waiting for device" your driver wasn't successfully installed. Close the Command Prompt window and open Device manager while your phone is still plugged in. (Search for it using the search option).

Right Click the "Android" option and select Update Driver. Choose to "Browse My Computer" and "Let Me Pick From A List." Pick the Driver with the newest date and install it. Now retry the code above. Your phone will ask if you want to unlock it. Select "Yes" by using the volume keys and use power to select it. Now, navigate to "Recovery Mode" with the volume keys. Use power to select.

A screen with another Android will pop up. Press Volume Up and Power at the same time. Select Factory Reset. This process may take a few minutes. Be patient and let it work. Once finished, select "Reboot."

 Your phone is now unlocked!


[Part 1 - Profesional Way to Unlock & Root] - Prerequisite
[Part 2 - Profesional Way to Unlock & Root] - Unlocking the Bootloader
[Part 3 - Profesional Way to Unlock & Root] - Root