The Jelly Bean update for the Sony Xperia T first started pushing out at the very beginning of February to unlocked devices. Since then, in the UK, O2 started pushing it out around a week later, and next up is the turn of fellow uk carrier Three. Announced this morning via their official Twitter account, Three has begun pushing out the Android 4.1.2 update to owners of the Xperia T on the network. Interestingly, Three's official support pages state that the update requires the latest version of the Sony PC Companion software, with no official mention of an OTA update. Sony themselves initially said that in some instances the update may only be available in this way, so it's definitely worth making sure you have the software installed on your computer.
Beyond the standard Jelly Bean features such as Project Butter and Google Now, Sony's update brings about changes to some of their own pre-installed apps. Walkman, Album and Movies all see redesigns, the homescreen has new personalization options and improvements are also made within the camera application.