Some new firmware has started rolling out for the Sony Xperia S (LT26i). Firmware version 6.1.A.2.55 has not appeared on the PTCRB website so far, but despite this it is now available to download in Singapore. Changes over the current firmware version (6.1.A.2.50) are unknown right now, although it does seem to be using a new baseband. This Android 4.0.4 ICS version cannot be rooted either using the existing root method from Bin4ry over at XDA.
Thanks Akshay & LiveSquare!