Thanks to LastStandingDroid over at the XDA forums, the Samsung Galaxy S II (I9100) has received an Android 4.1 Jelly Bean SDK port. With any SDK port, the build is fairly rough and one should expect many things to either not work, or not work correctly. Although there is a short list of things that do work:
SD card (internal-only)
MTP (can’t copy files)
While it’s great that certain aspects of it do work, there is quite a laundry list of things that don’t work such as audio (can’t use it as a phone), WiFi, Bluetooth, camera, GPS, etc. An SDK ported ROM is never meant to be used as a daily driver, it serves more or less as a way for a user to preview the new firmware. Of course, your phone needs to be rooted and have a custom recovery installed in order to flash this. Head over to the source link for more information.