Yes you heard it right....
Nexus S GSM phone update for Android 4.0 aka ICS(Iceream Sandwitch) is OUT...
Here's the method to get it.... ;D
1. Download this to your SD card of your phone. Link
2. Re-name it to update, and put it at root node in SD card.
3. Power off the device and then restart your phone with pressing volume up button.
4. Select recovery and press power button
5. Once the triangle appears, press power key and press volume up button.
6. Select the apply from sd card and choose update.zip.
7. Once done simply reboot.
Congratulations you are new ICS owner.