A lot of sites, and I mean a LOT of sites are saying that there is indeed a jelly bean port from the SDK to the nexus s 4g, it is supposed to have no sound/3g data, but that is roughly it, this is NOT true. This link from the XDA forums has a link within it that claims to have wifi working, that is not the case. Please read the entire thread before downloading. The thread says that NO wifi version has been uploaded and that is probably won't be because they wanted to fix all the issues before a build is released, here are the things it claims to have working, it sounds tasty.
I will post in this thread daily with answers and that kind of shizzle.
-Wifi (thanks to steven676)
What Doesn't Work:
-Ambient Light Sensor
-Other stuff I dont yet know about.
This is not quite true. The dev wanted to put wifi in and just never did, he did indeed go to sleep with plans to upload the wifi version, it sounds like while he slept others got 3g/data and wifi working, however, no one ever got sound working and Google Now did not work due to this limitation. The build does work like butter, pun intended. If you want to go there and download it to see how it works, please do, but do not expect much to work and always back up your previous work!
THIS IS NOT RECOMMENDED FOR THE FAINT OF HEART.
We are NOT responsible for anything that happens to your phone when rooted or with this build.