Sony started the rollout for Android Jelly Bean (4.1.2) on Xperia T. If you are willing to upgrade now and the update is not yet available for you on PC Companion there is a very simple way to do it. Be aware that I am not responsible for any damage you are going to do to your phone. In case you brick your phone try to find help on XDA developers forum. First, you have to download the software image from here: 0B_Oc…it-usp=sharing. In case link is not working let me know with a comment below and I will give you a private link. Then you need to apply it with Flashtool (in case you don’t have Flashtool, you can install it from here: http://androxyde.github.com/). To apply it you need to connect the phone in flashmode (phone powered off, keep volume down while connecting to USB). Use below settings to flash it:
When flashing is finished disconnect the phone and reboot it. First boot it will take some time. In case you need support or you have qustions you can address them here or on this forum: http://forum.xda-developers.com/showthread.php?t=2128733. According to this forum the procedure should work for both locked and unlocked bootloaders. Below I added some screenshots for the curious.
Besides the updates that comes with Android 4.1.2 this software brings HDR on camera (info about HDR here: http://en.wikipedia.org/wiki/High_dynamic_range_imaging) and Clear Audio+. I have tested it only one day so I cannot tell more about the update. Up to now it feels smooth and fast. Be aware also that after major software firmware upgrades the battery might drain faster for few days.