Google has only released a preview build of Android 4.1 Jelly Bean for the Play Store variant of the Galaxy Nexus and the Android community has already managed to get the build to work on non-Play store variants of the Galaxy Nexus along with the Nexus S, HTC One X, Galaxy S III, and now the Galaxy S II.
Like any non-source based port though, this port of Android 4.1 Jelly Bean barely works on the Galaxy S II. Nearly all the basic hardware features like Wi-Fi, GSM data, Camera, and external SD card don’t work. However, the developers should hopefully manage to get Jelly Bean up and running on the Galaxy S II once the latest version of the OS is pushed to AOSP. Until then, if you are jealous of your Galaxy Nexus-owning friends and cannot wait to give Jelly Bean a try, head over to this link.