Sony offers Jelly Bean ROM for advanced developers with an unlocked Sony Xperia T9
limited functionality. For example, you will not be able to make phone calls with it installed on your phone. Sony says that this update is for advanced developers only and if you do not know what you are doing, you are on the way to bricking your phone if you flash the ROM to your device. You must have an unlocked Sony Xperia T and must use Sony's Unlock boot loader service and agree to all conditions. As usual, you will most likely lose any warranty on the phone once it is unlocked.
The following statement is important. If you unlock your phone, you will not be able to receive the final version of Jelly Bean when it is ready to be disseminated by Sony. Some of the features that will be turned off if you flash the ROM on your Sony Xperia T is Gmail and Google Maps, any phone service, Bluetooth, Wi-Fi, NFC and the FM radio. The UI will not reflect the final Jelly Bean look and feel that the update will have when it is officially released. So what is on the ROM? Sony says it includes a number of Jelly Bean features that it knows developers will enjoy.
If you're interested in giving Sony some input on Android 4.1, you can use Sony's flash tool for unlocked Xperia models. All the directions can be found at the sourcelink. We'd suggest that if you aren't an advanced developer, your best bet is to stay on the sidelines and leave this to the experts.
source: SonyMobile via Engagdet