The short answer is that the update is released in stages.
An initial group of devices are selected at random and offered the update. This lasts for 3 days, Samsung use this process to ensure the update is being released succesfully and that the servers are delivering the update properly.
After those 3 days the update is available to all users when doing a manual check for updates, but once 10% of devices have received the update access is stopped for the remainder of the day. This is to ensure servers aren't overloaded and that those who get the update receive it succesfully.
After 10 days (that's 10% per day) everyone has had access and the update is available freely to everyone to download.
It's around 14 days from the initial release before every device will see the update as available.
Please see the table below for specific details on the roll out:
Day 1-3: 10,000 users will receive a notification to advise the software is available. The roll out will be monitored to ensure that server performance is maintained.
Day 4-13: The software will be made available to all users, however it is only available up to a maximum download volume representing 10% of the total installed userbase per day
Day 14 onwards: The update is broadly available to all users via either Kies or FOTA
From 12:00 (midday) today, 2nd May 2012 – Samsung will began rolling out the Android 4.0.3 “Ice Cream Sandwich” update for the GALAXY S II handset.
This is a platform upgrade and will change the way you experience and interact with your device. For more information about the interface changes introduced in this update, please contact Samsung Customer Care on 1300 362 603 or via any of the methods listed on here on their website.
What's included in the update?
Android 4.0 "Ice Cream Sandwich" introduces a many new fetures, bug fixes and enhancements, including:
Speed and performance enhancements
Folders of your favourite apps right on your homescreen
Improved keyboard input and error correction
Face Unlock - unlock your phone with a smile
Data Usage Meter
Improved voice detection including voice typing
Enhanced multitasking interface
Resizable homescreen widgets
Things to do before you upgrade your software
Ensure your device is fully charged before attempting to upgrade.
Remember to back up any important information prior to the performing the upgrade
How do I install the update? (For Vodafone-branded Devices)
This update is available using either Samsung's Firmware Over-the-Air (FOTA) update platform or the Samsung Kies PC companion software. This means you have the choice of not using a PC to perform the update.
Updating via FOTA
You can check for updates by navigating on your phone to Settings > About Phone > Software Update > Check for Update
The update is available free of charge, and should you choose to download it using 3G data within Australia and while using a Vodafone SIM card, the data will not be deducted from your monthly allowance.
If you update your device while on any roaming network, or you use a non-Vodafone AU SIM card, you will be charged at your applicable data rate.
The update is available free of charge, however you will need an internet connection on your PC to download and install both Kies and the update itself.
Please plug your phone directly into your computer via USB and not via a USB hub or repeater.
The update is approximately 1050MB in size when completed via Kies
A full PDF guide for performing the back up, software upgrade, and data restoration process is available by clicking on this link.
What are the technical details?
3.0.15-I9100TDULP9-CL422302 dpi@DELL149 #3
How do I install the update? (For 3-branded Devices)
For devices sold by 3 (regardless of the SIM card currently being used) the update is only available using the Samsung Kies PC companion software. This means you will require a PC to perform the update.