The bad news is, Sony smart phone development team has confirmed that they wont be bringing the ice cream sandwich update / upgrade (android 4.0) to Sony XPeria Play device.
In regards to Xperia PLAY, after extensive in house testing with our developer teams and working with our partners, we have concluded that a consistent and stable experience, particularly with gaming, cannot be guaranteed for this smartphone on Ice Cream Sandwich – therefore, we will not make the Android 4.0 upgrade available for Xperia PLAY. – Sony smart phone Blog
How ever, as always with android, you get the chance to root the device and treat it like a PC where you get to chose what OS you install hence even with XPeria play also there are many 3rd party options to let you install the latest android update / upgrade, namely ice cream sandwich (Android 4.0).
First, Download ICS Android 4.0 Zip package.
Then, Connect your phone to the computer using the USB Data Cable.
Next, copy the downloaded zip file (DooMLoRD-PLAY-GSM-ICS-4.0.3-ROM-LEAKED-v01.zip) to the root directory of your SD card.
Disconnect your phone to the computer and boot it in Clockworkmod Recovery.
If you don’t have a CWM Recovery, just follow the method of installing CWM Recovery here.
Once your in Clockworkmod Recovery make a Nandroid Backup just incase something goes wrong, you can restore it back easily. To do this, from the main menu select Backup and Restore> Nandroid Backup.
Then, go back to main menu select “Wipe data/factory reset” and “Wipe cache partition”.
Next, go back to main menu and select the option of Install zip from sd card> Choose zip from sd card> then choose DooMLoRD-PLAY-GSM-ICS-4.0.3-ROM-LEAKED-v01.zip to start updating your phone to Ice Cream Sandwich Firmware.
Finally, after a successful update go back to the main menu and select Reboot System Now.
Congratulations you can now enjoy your newly updated phone.