Way back in December 2011, Sony began releasing 'alpha' developer ROMs for some of its phones being upgraded to Android 4.0. Then it released beta ROMs that did slightly more stuff. Now it's done the same with Android 4.1 for the Xperia T.
These ROMs are developer-facing in every sense of the word, though, and aren't intended as a way for power users to get early access to the next version of Android. Most things that consumers, you know, use, are turned off.