The official update for Sony Xperia U is still under development and if you're tired of waiting for it to be released, you can update it yourself to Android 4.1.2 Jelly Bean custom ROM based on the AOSP version.
Sony is rolling out ICS update for Xperia go, Xperia Sola and Xperia U.
Sony Xperia U is viable for Android 4.1.2 Jelly Bean update using a custom ROM with build 6.2.A.0.400 firmware. Since the official update hasn't been released yet, why stress yourself if can get all the Sony applications, features and Jelly Bean goodness.
This must be flashed only to Sony Xperia U ST25. Do not install this custom ROM to other devices or suffer the consequences.
Your Xperia U must be unlock to flash this custom ROM.
Create a backup of all your personal information, settings and data files on your phone.
Warning: This is a custom ROM and should only be flashed to the right phone model. Developers are not liable for any damages which may occur on your device. Read and follow the instructions carefully to prevent any errors during installation. Do this at your own risk.
Go to step by step: Flashing Instructions
1. Extract the files from the Fastboot zip you have downloaded earlier.
2. Extract the downloaded ROM containing "boot.img" file and copy it to the fastboot file folder.
3. Copy the downloaded custom ROM and the Fix zip files to the Xperia U's internal memory.
4. Switch off the device and wait till the shutdown is complete.
5. Connect the device to the computer via USB cable while pressing Volume up key. This will bring your phone into fastboot or bootloader mode.
6. Go to your computer and open the fastboot folder.
7. Press and hold the shift key then right click inside the fastboot folder to open the window context menu. Select the "open command window here."
8. Type in this command line on the command window: fastboot devices
9. It should display "xxxx xxxx fastboot device" message confirming that the device is detected. Otherwise, reinstall the ADB drivers, disconnect your phone and reconnect it again.
10. After the confirmation, type in this command line: fastboot flash boot boot.img
11. Once "finished in..." is displayed, disconnect your device.
12. Switch on the power of the Xperia U.
13. Press continuously and release the Volume Up key once you see the Fist Logo. This will boot the device into recovery mode.
14. Inside the ClockworkMod recovery, perform an Android backup to save your current ROM. Go to "backup and restore > backup."
15. Perform a full wipe on your device. Select "wipe data/factory reset" and "wipe cache partition." Confirm both selections.
16. Perform the Dalvick cache wipe, go to the main menu, select "advanced > wipe dalvik cache."
17. Go back and select "install zip from SD card > choose zip from SD card." Choose the custom ROM you have copied on your device.
18. Once the installation has been completed, go back and select "reboot."
Well done! Your Sony Xperia U is now running Android 4.1.2 Jelly Bean with this custom ROM. If ever you wanted to go back with the previous ROM, follow theAndroid backup and restore link .