Before you begin, please make sure that your device is on at least 75% battery. If your device dies during this process, it could potentially be damaged or bricked.
Disclaimer: Unlocking the Bootloader of your device will factory reset it. Make sure you back up any important data. Unlocking the bootloader will void the warranty. If by using this guide your phone is somehow damaged or bricked, I will not be held responsible or liable in any way. This guide is only to be used for the Xperia Miro. This is something you are doing at your own risk and of your own free will.
1. Make sure it’s actually possible for you to unlock your Xperia Miro. To do this, go to the keypad for the phone. Type in *#*#7378423#*#* in order to get to the service menu.
2. On your device, go to Service info>>Configuration>>Rooting Status. If Bootloader unlock allowed says yes, then you can continue. If it says no, your device cannot be unlocked.
3. If you can infact unlock your device, go here, and click Yes, I’m sure.
4. Make sure you read through the terms and conditions before you click I accept.
5. Create an unlock boot loader key request on the form. (Enter your name, a valid email address and the IMEI (or MEID) number of your device. You can view this number by entering *#06# on they keypad of your device.
6. The unlock boot loader key will be sent to the email address you provided. SAVE the email.
7. Download the latest Android SDK and install it. You can get it from here.
8. Download this file. Unzip the file and place it in the usb_driver folder, which you can find in the Android SDK>>extras>>google folder on your computer. Accept the request to replace the old android_winusb.inf file.
9. Turn off your Xperia Miro.
10. On your device, press and hold down the volume up button as you plug it in to your PC. When asked for drivers, go to the usb_driver folder where you put the android_winusb.inf file. Select the Android Boot Loader Interface file.
11. Go to the tools folder inside of the Android SDK folder and open a command window. You can do this by pressing shift and right clicking on the window. Select Open command window here.
12. Enter fastboot.exe -i oxofce getvar version and make sure you get a response. (ex. 0.3)
13. Enter fastboot.exe -i oxofce oem unlock oxKEY - where KEY is the unlock bootloader key that was emailed to you.
14. The bootloader should now be successfully unlocked.