In the past couple of days, numerous Samsung Galaxy S3 updates were leaked, one of the latest is software version UVDLI8 of Android 4.1.1 Jelly Bean for the T-Mobile variant (SGH-T999). XDA Developers member djintrigue808 has taken advantage of the leaked OTA update and crafted his very own custom ROM known as FrostyJB.

FrostyJB is pretty much the same as the UVDLI8 Jelly Bean ROM leak, but it has been modified so that it can easily be flashed using ClockworkMod Recovery.  Basically, all the essential Jelly Bean features are present in the ROM like the smooth buttery interface, Google Voice, smarter keyboard, and the faster web browser. What's even better is that FrostyJB is already rooted and has also been stripped of all T-Mobile bloatware.

This guide shows you how to upgrade the Galaxy S3 T999 to Android 4.1.1 Jelly Bean via FrostyJB custom ROM.

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.
  • Need help with installing ClockworkMod Recovery? You can refer to this guide:
    • Samsung Galaxy S3 SGH-T999 (T-Mobile): How to flash ClockworkMod Recovery
• Download the FrostyJB ROM (FrostyJB_4.1.1-M2.zip, md5sum: 8B79FE8E0083468C83A565812C273CF628) — also available from a mirror link
• Fully charged battery or at least 70% battery left
• 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 FrostyJB ROM ZIP file to your phone's internal SD card.
2. Switch off your phone.
3. Boot into ClockworkMod Recovery. You can do this by pressing and holding down the Volume Up, Home, and Power buttons together until your phone screen turns on.
   • NOTE: Use the Volume buttons to navigate and Power button to select an option in recovery.
4. Create a NANDroid backup of your existing ROM. To perform a backup, select Backup and Restore and on the next screen, select Backup again. Head back to the main recovery after backup is complete.
5. Select Wipe data/factory reset, then select Yes on the next screen to confirm data wipe.
6. Select Wipe cache partition and confirm the action on the next screen.
7. Go to the main menu and select Advanced. From there, select Wipe Dalvik cache and confirm the action on the next screen.
8. Select Install ZIP from SD card, then select Choose ZIP from SD card. Browse for the downloaded ROM file and select it. Confirm the installation by selecting Yes on the next screen. The ROM will now start installing on your phone.
9. Repeat steps 6 and 7.
10. Go to Advanced and select Fix permissions.
11. After the ROM finishes installing, head back to the main recovery menu by selecting Go back then select Reboot system now to reboot your phone.
12. Once fully booted, leave your phone untouched for about 5-10 minutes and then reboot your phone.

Congratulations! You have successfully installed the FrostyJB ROM on your T-Mobile Samsung Galaxy S3 SGH-T999.