Samsung Nexus S: Flush Jelly Bean Factory Image

I have been waiting for OTA for several months with no luck. So finally decided to flush my Samsung Nexus S with Jelly Bean 4.1.2 factory image. Here is how I did it. 

1. (PC) Download Nexus Root Toolkit from here (don't worry. I did not root my phone, just unlocked it for flushing!). 
2. (PC) Install the software. When prompted, choose your device. In my case, it was Samsung Nexus S, 850MHz, i9020a. Allow the software to download necessary files for your phone.
3. (PC) Connect your phone to the PC with a USB cable. Run the 'Nexus Root Toolkit' software and click on 'Unlock'. Follow the on screen instructions to unlock your phone.
4. (PC) Download Nexus S factory image from here. 
5. (PC) Unzip the downloaded image in the installation directory of Nexus Root Toolkit. In my case the path was C:\Program Files\WugFresh Development\data
6. (Phone) Turn off your device 
7. (Phone) Go to Bootloader (press&hold volume up button then press&hold power button) 
8. (PC) Go to the folder where you unzipped the factory image. Make sure that the folder contains adb.exe and fastboot.exe.
9. (PC) Double click on flash-all.bat file. This will flush the factory image in the phone.
10. (PC) When done, click on 'OEM Lock in the Nexus Root Toolkit to lock bootloader again.

Enjoy your Jelly Bean:)

Samsung Nexus S i9020a: OTA Update to JB 4.1.1 from 4.0.4

Several user have reported the following procedure as successful, but some failures were also reported. Try at your own risk:)

1. Connect your charger! This is a prerequisite
2. Go into airplane mode
3. Under settings->apps->all (scroll the page to the left), 
• select 'Google Services framework'
• force stop it and 
• then delete its data



Enable wifi only (don't leave airplane mode)
Settings->about->system updates->check for update.

Repeat this several times if it doesn't work at first. There is no need to remove the sim card or  reboot.