The long wait is over now as Ice Cream Sandwich 4.0.3 is coming to Nexus S officially. The news is released by Google. You can update your Nexus S manually. To install Ice Cream Sandwich 4.0.3 on Nexus S follow the instructions.

Before you start make sure your phone battery is charged up to 60% and backup your data in your computer. Now turn on USB Debugging. Then go to Menu =>Settings => Application => Development.

Requirements:

1. T-Mobile Nexus S
2. USB Data Cable
3. Computer

Instructions:

1. To get star download OTA package. You can download it here.
2. Now rename the downloaded file as “update.zip”
3. Now connect your phone to your computer
4. Now copy the renamed downloaded file “update.zip” to the root of your SD card.
5. Now after copied disconnect your phone and turn it off.
6. Now head to the bootloader. To do so press the power and the volume up button simultaneously. 
7. Once you are in the bootloader select “Recovery”. To do so press the volume up and down and to select, press the power button.
8. Now a warning Android logo will appear on your screen. Now go the “Menu”  by pressing volume up button and power button again.
9. Now from Menu select  “Apply update from /sdcard” and then choose “update.zip” from the list.
10. Now your phone will be updated by itself.
11. After finishing go back and select “reboot”.
12. You have now updated your Nexus S to Ice Cream Sandwich 4.0.3