The CyanogenMod team is working day and night to brew and serve the freshest CyanogenMod 10 custom ROM, which is based on Android 4.1.1 Jelly Bean. The team also released a preview build to give users a glimpse of how the new ROM would feel on your mobile phone. One of those lucky phones is the T-Mobile Samsung Galaxy S3 SGH-T999.

Team Cyanogen shared a preview build of CyanogenMod 10 for the T-Mobile Galaxy S3. Although the ROM is still in its early stages and contains bugs, this ROM will let you see how cool Android 4.1.1 Jelly Bean is on your mobile phone.

Take note that this ROM is only a preview build of CyanogenMod 10 and not (yet) recommended to be used as a permanent or daily ROM.

Read on to learn how to flash CyanogenMod 10 for the T-Mobile Galaxy S3 SGH-T999.

Warning

• The instructions in this guide are intended for use with the T-Mobile Samsung Galaxy S3, model number SGH-T999. 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

• T-Mobile Samsung Galaxy S3 SGH-T999 with ClockworkMod Recovery installed.
  • Check our guide on how to install ClockworkMod Recovery on your mobile phone.
• Download the following files:
  • cm-10-20120720-UNOFFICIAL-d2tmo.zip (153 MB)
  • gapps-jb.1.zip (103 MB)
• 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 cm-10-20120720-UNOFFICIAL-d2tmo.zip and gapps-jb.1.zip to your phone's internal SD card.
2. Switch off your mobile phone.
3. Reboot your phone into ClockworkMod Recovery Mode. You can do that by pressing and holding down the Volume Up key, Home button (middle key), and the Power button simultaneously until recovery boots. 
   • NOTE: Once in recovery, use the Volume keys to navigate and the Home button to select an option.
4. Create a NANDroid backup of your current ROM. Select Backup and Restore and select Backupon the next screen.
5. Select Wipe Data/Factory Resetand confirm the action on the next screen.
6. Select Wipe Cache Partition and confirm the action on the next screen.
7. Go back to the main menu and select Advanced. From there, select Wipe Dalvik Cache and confirm the action on the next screen.
8. Return to the main menu and select Install ZIP From SD Card.
9. Select Choose ZIP From SD Card and locate cm-10-20120720-UNOFFICIAL-d2tmo.zip file. Confirm the action on the next screen to flash the ROM to your mobile phone.
10. After installation is complete, go back and flash the gapps-jb.1.zip in the same manner as in steps 8 and 9.
11. Go back to the main menu and select Reboot System Nowto restart your phone.
12. To revert to your previous ROM, reboot your phone into ClockworkMod Recovery and select Backup and Restore.On the next screen, select Restore to install your previous backup ROM.

Congratulations! You have successfully flashed the CyanogenMod 10 preview build on your T-Mobile Samsung Galaxy S3 SGH-T999. You finally have a glimpse of what it feels like to run Android 4.1.1 Jelly Bean on your mobile phone.