Jelly Bean arrives over-the-air for some Google Nexus S phones
Right now, it seems that the Google Nexus S with model names i9023 and i9020T are getting the update, with some devices in Asia landing it first.
The update weighs 114MB and bumps the Nexus S up to version JRO03E. Of course, you shouldn’t lose any of your data during the update.
source: XDA Developers