Samsung have just pushed the Android 4.0.3 (Ice Cream Sandwich) update for the Galaxy S II on Optus to Kies. The update may be available for download over-the-air (let us know in the comments) or you can download it via Samsung Kies 2.0.
Optus is the first carrier to launch the new update, so props to them for the quick(ish) release. There’s no doubt Telstra and Vodafone will be releasing the update very soon as well, so keep an eye out.