JB ROM in testing for Xperia P, flash at your own risk
If you own an Xperia P and are eager to flash it to Jelly Bean, now is the time. An Android 4.1.2 Jelly Bean ROM with Firmware 6.2.A.0.399 has leaked. It's meant for internal testing on developer Xperia P units but has been found to work on production units.
The ROM isn't final yet and there are things missing or not working on it. Therefore, we advise you to flash at your own risk and MAKE A BACKUP. Also a prerequisite is that you need to either be running a stock ICS ROM or a ROM based on stock AOSP one in order to flash this one. Your bootloader will also need to be unlocked.
Other than that - copy the ROM into your memory, reboot into recovery and flash away.
There's no information yet on when an official release will hit the Xperia P.
Thanks, Ben Ling for sending this in!Source