The Sony Xperia S is scheduled to receive ICS at the end of the month but thanks to SonyXP we get to see the Sony flagship running the latest Android version earlier. (says GSMarena)
I made some research and actually I found two alternatives for ICS running on Sony xperia S. But let's take events one of the time.
See more for a video and links to download Sony xperia S ICS [ROM].
Video with ICS working on Sony xperia S:
And let's pass to a place where you can always find some skilled boys doing a grate job. XDA developers.
1 GNexusTimeScape [ROM] HERE download ICS for Sony xperia S and we have some preview. I tested this ROM, easy to install if you are familiar with flashing custom ROMs and it is OK as long you don't need NFC, Video Recording and Video Playback. Off course those small details can be easily left behind with some free apps from Google Play.
2 Xperia S AOKP [rom] HERE download ICS or Sony Xperia S I didn't tested this ROM yet, but I have tested Resurrection Remix ROM for galaxy S2 made by same developer AOKP and they usually do a very good job. They won they'r trust a long time ago by creating two of the best ROMs for galaxy s2. 100% Trust from me and recommendation for you.
So if you can't wait for official release update, that will be released later then the half of the year (at the end of Q2) You can test those two ROMs earlier.