However as many other people I still do not have one yet. So fro the inpatient here is a tutorial how to install it yourself.
Prerequisites:
1) Installed official Android 2.3.4, 2.3.6, 4.0.3. To update manually to 4.0.3 from any version check here: http://andwise.net/?p=70
Note that this is not a full update but a patch so you really need to have original(not modified) 2.3.4, 2.3.6 or 4.0.3 installed before.
2) CWM recovery, you can check how to do it here: http://andwise.net/?p=268 (only if you are updating form 4.0.3)
3) download the update from google (we will call it update.zip):
for 4.0.3(IML74K/XXKI1 Radio)->4.0.4 - http://android.clients.google.com/packages/data/ota/google_crespo/hR7QFEtn.zip
for 2.3.6(GRK39F/XXKF1 Radio)->4.0.4 – http://android.clients.google.com/packages/ota/google_crespo/fL9fwa99.zip
for 2.3.4(GRJ22/XXKD1 Radio)->4.0.4 – http://android.clients.google.com/packages/ota/google_crespo/RYyRmqNv.zip
Note: these are for i9020T/i9023, for i9020A from 2.3.6(GRK39F/UCKF1 Radio) use : http://android.clients.google.com/packages/ota/google_crespoa/IEzMw3FU.zip
for up-to-date info check: http://forum.xda-developers.com/showthread.php?t=1063664
Procedure:
1 ) Put it update.zip you have downloaded on your sd card.
2 ) Turn off your device
3 ) go to Bootloader (press&hold volume up button then press&hold power button)
4 ) when in Fastboot mode navigate to [Recovery] using volume up/down buttons
5 ) Press the power key to select [Recovery]
6 ) If you see a warning logo, press the power button and then press volume up button then release both to go to the Main Recovery menu (this step is needed mostly for the stock recovery images)
7 ) From the menu, select [Apply update from /sdcard], and choose update.zip from the list.
8 ) When update is finished go back and select [reboot system now]
Enjoy 
Is it considered as rooting up the phone? And is it valid for rooted phones only or for non rooted ones also?
This will not root the phone. These links just points to official OTA updates. As it says on top you need to have the official build before doing this update otherwise you get an error.
Thanks a lot, andmin, one last thing to confirm, is this update applicable for Google Nexus S i9023, India, with official Android 2.3.6?
if it is the same build as stated in the links yes
hi there,
i did exactly as you told, upgraded to ics but it is now not showing the imei number and not recognising the network…… what should i do now? is there a way to undo the incremental update or is there a solution to fix this???
please help me…
did you make a backup? what is your phone exactly?
2.3.6 -> 4.0.4 Thanks a lot, works just fine..keep up the good work.
any such update from android 2.3.3, baseband i9023xxkb3, nexus s i9023 to android 2.3.6 ???? please help, the samsung service center guy degraded my phone from 2.3.6 to 2.3.3!!!
you need to flash a full rom for this baseband
you can update to 4.0.3: http://andwise.net/?p=70
then to 4.0.4. don’t forget the backups!
I have Nexus i9023. I am not able to go to Recovery, as it is showing a black screen. when i look closely i can see a droid animation lying down position. How can i navigate and choose “update”.
I did manual update of 4.0.3.
Build Number: IML74K.
Stock ROM
you need to instal CWM recovery to update from 4.0.3: http://andwise.net/?p=268
Hi. I have a Nexus S in Romania (i9023), with official 2.3.6, baseband version I9023XXKF1, build number GRK39F.
Can I use 2.3.6 -> 4.0.4 – fL9fwa99.zip? I didn’t see anything about build number in the above links.
yes you can. build/radio added thx
Thank you. I’ll give it a try
It worked flawlessly (official 2.3.6 to 4.0.4). Thank you for the guide
Thank you so much andmin!!! I got the 2.3.6. OTA last night on my 2.3.3, then in the morning I downloaded the patch from this link of yours, and here I am tasting the delicious Ice Cream Sandwich!!! And this whole process took me less than 6-7 minutes!!! Would I be able to get the other OTAs on this version?
yes you will. you practically have OTA also now
Hey andmin, dude, they din’t give us face lock, screen shot and face recognition for camera in this update, did they?
Hey buddy! Hows life? Hey, do you have the Google Nexus S i9023 Jelly Bean update? If yes, then please send me the link. I would highly appreciate.