A german Sony representative announced on their official Support Forum that an update to Android 4.0 Ice Cream Sandwich OS is coming to both Sony tablet S and P in the near future.
Recently Sony released the Software Development Kit (SDK) for the Sony Tablets and Android 3.2.1 Honeycomb software update. We should expect Android 4.0 arrival as early as next year somewhere in January, maybe in late February. The very same representative also added that more information about these updates and future beta upgrades can be found on Sony Tablet Evolution website.
source Sony [DE]