The Ice Cream Sandwich firmware includes improvements to: stability, WiFi, tethering/portable hotspot, camera (capture and playback), NFC and Messaging
It’s not clear precisely which version of Android 4.0 will be released. From information on Sony’s update pages, it appears the build number of the new software is 6.1.1.B.1.54.
As with most software updates, availability will vary by carrier and region. It looks like Sony has announced the updates and released them for the carrier-free versions of the devices, but may not have submitted the update to local carriers yet.
While Australian carriers don’t have any mention of these updates on their sites, Vodafone’s November 29 updates list a “4.0.4 maintenance release” for the Sola which has completed testing and is now undergoing review. It seems unlikely that this is the update Sony has just revealed.