Are you a owner of AT&T Galaxy S3 and wanted to install/update Cyanogenmod 9 firmware on your device then today I am going to tell you about this update using a simple process. This update is based on nightly official development build.

Cyanogenmod 9 firmware on AT&T Galaxy S3

This update will fix some common things like USB, Camera and Voicemail issues. But, please not that the update I am going to tell you is just for educational purposes, so use it at your own risk.

1. Backup all your data.
2. Ensure that your battery is above 70% or else connect your device to the charger.
3. Enable USB debugging feature by tapping Settings->Applications->Development.
4. Download ROM from official development site.
5. Download Google Apps.
6. Copy both the files to your SD card.
7. Switch off your device and restart by pressing Volume Down + Home + Power button for Recovery mode.
8. Select wipe data / factory reset option and let the wiping complete.
9. Now, select “Install zip from sd card” and then “choose zip from sd card” and then select the ROM file you just copied on step 6.
10. Perform the same step 9 for Google Apps.
11. Wait for the installation to complete and then restart your device.

That’s it, your device is now updated with Cyanogenmod 9 firmware nightly build.