For those of you who want to root your T-Mobile Galaxy S3 SGH-T999, here’s a specific fail-safe noob guide.
Step 1. Hold down Volume Down, Center Home, and Power button together for about 10 seconds until your phone reboots.
Step 2. Let go of only the Power button when your phone resets. You should see a warning screen like below:
Step 3. Press Volume Up to enter ODIN Download Mode then connect a microUSB cable from your T-Mobile Galaxy S3 to your computer.
Step 4. Download GalaxyS3RootSprint.zip and unzip, you should find 4 files like below under GalaxyS3RootSprint.
Double-click on the ODIN EXE file to run the ODIN program.
Step 5. You should see a yellow-highlighted box with random COM number. If you do, you are good to go. Otherwise, you don’t have the correct Galaxy S3 drivers, download Samsung Kies and install it. Then unplug/plug your phone and you should see it now. (Also turn off Kies program, don’t have it running at the same time with ODIN!)
Step 6. DO NOT TOUCH ANYTHING ELSE but hit the “PDA” button, choose the file “clockworkmod.TAR” and hit “Start”.
Step 7. This will flash ClockworkMod Recovery into the Recovery partition of your T-Mobile Galaxy S2 SGH-T999 then your phone will reboot.
Step 8. Once rebooted, copy the file “CWM-SuperSU-v0.87.zip” to anywhere on your Galaxy S3.
Step 9. We will now reboot into ClockworkMod Recovery, hold down Volume Up, Center Home, and Power button for about 10 seconds.
Step 10. Once your phone reboots, only let go of the Power button.
Step 11. Once in ClockworkMod Recovery, choose “install zip from sdcard” and hit the Power button.
Step 12. Next choose “choose zip from sdcard”.
Step 13. Next choose “CWM-SuperSU-v0.87.zip”.
Step 14. Next choose “Yes”. This will install SuperSU superuser app and root your phone.
Step 15. Once it’s done, simply reboot and you will have root!
Q: Does this root method erase my settings and apps?
A: No, it doesn’t touch a thing, very safe to do.
Q: I ended up in Kernel panic mode, what do I do?
A: Relax, that’s same as ODIN download mode, simply run Heimdall again and flash the files again, it will work.
Q: I don’t get ClockworkMod Recovery like you do, just get Android with belly open.
A: If you’ve updated to newer software update, the stock OS will over-write ClockworkMod Recovery on reboot. To fix this, make sure “auto-reboot” is checked off in ODIN, then take the battery out when it’s done flashing in ODIN. Then enter ClockworkMod Recovery right away.
More questions? Please leave in the comment section below for help from author and other users.
More on this Root Method
This root method simply installs ClockworkMod Recovery to the recovery partition and installs Superuser zip file, very safe to do. With Galaxy S2, recovery partition was part of the kernel and was a bit dangerous but with Galaxy S3, Samsung has made recovery parition separate from the kernel, making it much safer just like how Galaxy Nexus works.