The HTC One Series will be the first devices to savor Android 4.0.3 Ice Cream Sandwich coupled with HTC Sense 4.0. But if you own a Google Nexus S you can try out the HTC's latest offering thanks to the RUU leak from the HTC One X.
The ROM is still in a pre-alpha stage of development, so don't expect all the features to work well yet.
NOTE - Installing custom ROMs in not recommended for novice users. Please do not proceed unless you understand these risks.
DISCLAIMER - This site and the developers of this ROM will not be responsible for any loss of data or device malfunctioning. Proceed at your own risk
- Download the custom ROM
- Place the downloaded file in /sdcard directory of your Google Nexus S
- Switch off your device
- Press and hold Volume Up + Power until you see the ClockworkMod Recovery
- Perform a nandroid backup using your custom recovery tool. You can use this backup to revert back if you encounter any problems.
- In the main menu
- Select Wipe Data to factory reset
- wipe cache partition
- wipe Dalvik cache under advanced menu
- Go back to the main menu
- Go to install zip from sdcard > choose zip from sdcard
- Select the zip file you download in step 1
- Once flashing completes reboot your device
If you have performed the steps correctly you will have Android 4.0.3 Ice Cream Sandwich with HTC Sense 4.0 on your Google Nexus S
source - XDA Developers