Not long ago the CyanogenMod team released a CM 10.1 teaser for Samsung Galaxy S3 i9300. As you may know, CM 10.1 is vanilla flavored Android 4.2, based entirely on AOSP. Fortunately for all Galaxy S3 users, CM 10.1 has been released in an unofficial state.
It’s not yet a stable build and shouldn’t be used on a day-to-day basis, but you can give it a try and see how it works for you. It also has a lot of bugs and it lacks a handful of features, unfortunately. Here are the known bugs: UI glitches and lag, Phone app bugs, touch to focus doesn’t work very well, FM Radio and TV Out don’t work at all.
It will be a tough job for them to make it work smoothly, because they lack Samsung’s hardware drivers, though CyanogenMod is known for being the best Android developer and they might release a relatively stable version in the following weeks.
If you can’t wait until Samsung releases an official Android 4.2 Jelly Bean update, which can take a few months, you can give it a try right now. We are preparing a guide to help your flash CM 10.1 on your Galaxy S3. But I want to advise you again: it’s really not very stable and you can’t rely on it very much. Here you have the guide to flash CM 10.1 on your Galaxy S3.
Samsung has just released the official Android 4.1 Jelly Bean update for the Galaxy S3 i9300, so you will definitely have to wait a couple of months for the 4.2. Hopefully it won’t take them too long, considering that it’s not an all-new Android version, but rather an improved version. It only comes with a few new features, like lockscreen widgets, Daydream ( screensaver ), and MHL, which allows you to share your device’s screen with a TV or another gadget that supports it.