Developers have been busier than bees the past few weeks for they have been working non-stop to let Galaxy S3 owners experience Jelly Bean on their device. Three out of the four U.S. variants (Verizon, Sprint, and T-Mobile) of the Galaxy S3 have received the official Jelly Bean-based CyanogenMod 10 (CM10) custom ROMs.

Jelly Bean features can now be previewed and enjoyed, thanks to the efforts of XDA Developers member cyanogen, the man behind one of the most popular and most used custom ROMs.

To complete the line-up, it is now the AT&T Samsung Galaxy S3′s turn to get a Jelly Bean preview build. And, because, this is still a preview build, expect some things to not work, such as the camera preview animations that have a tendency to crash. In a few days or so, these issues and bugs may be improved.

In the rest of this post, you will learn how to upgrade the AT&T Galaxy S3 I747 to Android 4.1.1 Jelly Bean via CyanogenMod 10.

Warning

• The instructions in this guide are intended for use with the AT&T Samsung Galaxy S3, model number SGH-I747. Applying these instructions on another device or model may produce undesired outcomes.
• The information in this guide is provided for instructional and educational purposes only. There is no guarantee that these instructions will work under your specific and unique circumstances.
• Use these instructions at your own risk. We shall not hold any responsibility or liability for whatever happens to you or your device arising from your use of the info in this guide.
• Read and understand the whole guide first before actually performing the instructions.

Requirements

• An AT&T Samsung Galaxy S3 with ClockworkMod Recovery installed
  • For help on installing ClockworkMod Recovery on your handset, check our guide on how to flash ClockworkMod Recovery on the AT&T Samsung Galaxy S3.
• Your phone's USB cable.
• Download the following files to your computer:
  • CyanogenMod 10 Jelly Bean Preview Build (cm-10-20120729-UNOFFICIAL-d2att.zip, 153 MB)
  • GApps (Google Apps) package (gapps-jb.1.zip, 103 MB)
• Make sure your phone's battery is charged up to 75% or more to avoid interruptions during the process.
• Backup all personal data on your phone to make sure you have a copy of your personal data (e.g., contacts, SMS, MMS, Internet settings, Wi-Fi passwords, and the like) in case the procedure in this guide erases such data.
  • For backup tips, check our guides on how to sync your data to the cloud and how to create local backups of your mobile data.

Instructions

1. Copy the two ZIP files to the phone's internal SD card.
2. Switch your phone off and boot into ClockworkMod Recovery. To do this, press and hold the Volume Up, Home, and Power buttons together until recovery boots.
3. Make a NANDroid backup of your existing ROM in case there will be problems. To perform a backup, select Backup and Restore and choose Backup. Go back to the main recovery menu after backup is done.
4. Select Wipe Data/Factory Reset and confirm the action on the next screen.
5. Select Install ZIP from SD card then select Choose ZIP from SD card. Select the cm-10-20120720-UNOFFICIAL-d2att.zip file. Confirming the action on the next screen will start installing the ROM to your phone.
6. After the installation is done, install the GApps package in the same manner as in step 5.
7. Once installation is done, select Go back and choose Reboot system now to reboot your phone to the newly installed CM10 ROM.

Great! Your AT&T Samsung Galaxy S3 is now running on Android 4.1.1 Jelly Bean via CyanogenMod 10 (preview build).