It is only compatible with devices with unlocked bootloaders
Sony has yet to release the long-awaited Android 4.1.2 Jelly Bean update for the Xperia U, but that does not mean that owners of the smartphone should wait until the Japanese company decides to go live with the promised upgrade.XDA-Developers forum member munjeni ported the official Jelly Bean ROM for Xperia go that was released last week, on the Xperia U.
The Jelly Bean ROM only works on Xperia U devices with unlocked bootloaders and is not intended for everyday use due to some bugs.
According to XperiaBlog, the camera is not functioning in this ROM and there are some issues with the rotation feature. The battery is said to be depleting faster than usual and the capacitive buttons are a bit buggy.
If you still feel confident and wish to download and install this unofficial Android 4.1.2 Jelly Bean port for Xperia U, head over to the original thread.