Unlock Xperia Play R800i for use with CM9 Is there any way I can unlock the bootloader for my O2 Xperia Play so I can install Cyanogen Mod on it? Sony announced today that they will not be releasing ICS for the Xperia Play. Now I want to unlock it and put Cyanogen Mod 9 on it. How would I go about doing this?
Unlocking Your Xperia Play

Known issues

It is currently not possible to unlock the boot loader for CDMA phones.
Some customers with unlocked boot loaders have experienced problems when they are accepting over the air upgrades (FOTA - Firmware upgrade Over The Air). For customers that have unlocked the boot loader, please do not accept any over the air upgrades. For additional information, check out the hints and tips from the community on the XDA forum.
Instructions


First, you should confirm that it is possible to unlock the boot
loader of your phone by checking the service menu. 
In your phone,
open the dialler and enter ##7378423## to access the service
menu. In your phone, tap Service info > Configuration > Rooting
Status. If Bootloader unlock allowed says Yes, then you can continue
with the next step. If it says No, or if the status is missing, your
device cannot be unlocked. 
On your computer, click Continue at the
bottom of this page to start the unlock boot loader process. 
Read
through the information in the pop up window and click Yes, I’m
sure,    if you are still confident you want to unlock the boot
loader. 
Read    through and accept the legal terms. Click I Accept.
Enter your name,    email address, the first 14 digits (remove the
last digit) of your    phone’s IMEI number and the two CAPTCHA words
in the input boxes.    Click Submit. You can view the IMEI number by
entering *#06# on your    phone. 
The unlock boot loader key is
displayed. Write it down and    save it for later use. 
Download and
install the latest Android SDK    from developer.android.com.
Download and unzip this file. This is the    standard
android_winusb.inf-file, with a few lines of code added to    enable
Fastboot to support Sony and Sony Ericsson devices. Make sure    you
are running Google USB Driver package revision 4 or higher in
your Android SDK. You can see current Google USB Driver package
revision in the SDK Manager. 
Place the unzipped file in the
usb_driver folder, located in the Android SDK > extras > google
folder on your computer. Accept to replace the old
android_winusb.inf-file with the new file. If you can't find the
usb_driver folder, please install the Google USB Driver Packager
using the Android SDK manager. 
Turn off your phone. 
On your phone,
push and hold the unlock button* at the same time as you connect the
phone to the computer with a USB-cable. The unlock button may differ
between different phone models. See the note in the bottom of this
page for more information on what button use on your phone. 
On your 
computer, you will be asked for drivers. Point to the usb_driver
folder where you placed the android_winusb.inf-file, and select the 
Android Boot loader Interface-file. 
Open a command window and go to 
the tools folder within the Android SDK folder. 
Enter fastboot.exe
-i    0x0fce getvar version, and verify that you get a response back (for    example "0.3"). This means your phone is connected properly.
Warning! If you perform this step, you will unlock the boot loader.    This may void your warranty and/or any warranty from your
operator.    If you still want to unlock the boot loader of your
phone, enter    fastboot.exe -i 0x0fce oem unlock 0xKEY, where KEY
is the unlock boot    loader key you got in the beginning of this
instruction. The boot    loader should now be successfully unlocked.


Hold the following button while connecting your phone to a computer with a USB-cable:


Menu button (for Xperia™ arc, Xperia™ arc S, Xperia™ neo, Xperia™ neo V, Xperia™ pro).
Search button (for Xperia™ PLAY).
Volume up button (for Xperia™ mini, Xperia™ mini pro, Xperia™ ray, Xperia™ active, Live with Walkman™, Xperia™ S).


This process was found on Sony's unlocking site.