Thanks to XDA member itsmikeramsay, Galaxy S3 owners on T-Mobile and AT&T networks can now install the beloved Cyanogenmod 10.1 (Android 4.2) on their handsets.

As with many early builds of custom ROMs some options donít work as intended and there are definitely some bugs and missing features. Bear in mind that as Android 4.2 is relatively new, chances are youíre going to run into a few unforeseen problems on unsupported devices. So unless youíre willing to live with a few bugs or willing to try and figure out some workarounds, itís probably not ready for everyday use just yet.
Still this is very good news for S3 owners as it opens the door for the Cyanogenmod to get behind Galaxy S3 development officially.
Unfortunately the CM10.1 ROM is still missing a working camera, tethering, MTP support, the headphone jack doesnít work during calls and the device will have sporadic Bluetooth functionality.
However, if you are going to install the ROM be aware that your internal SD card data will be moved to /storage/emulator/0 due to Android 4.2ís multi-user feature. Check out the T-Mobile or AT&T forum threads over at XDA-developers for the fileís youíll need.

SOURCES XDA Developers