It has now been confirmed that Sony has begun rolling out the Android 4.1.2 Jelly Bean update for the Xperia T devices in Netherlands. The update will carry a version number of 9.1.A.0.489, running on the 3.4.0 kernel. As for other countries, we have yet to hear any news about the update from them.
However for those who’ve yet to receive the Jelly Bean update, you can also try your luck by going to Settings > About phone > System software updates and manually check for the update.
Remember to share with us the improvements after you’ve successfully updated your device to Jelly Bean!
Source : Xperia Blog