Tips & Tutorials

Update T-Mobile Galaxy S3 SGH-T999 to Android 4.1.2 CM10 Jelly Bean Custom Firmware

T-Mobile Galaxy S3 SGH-T999 can now be updated to Android 4.1.2 Jelly Bean custom ROM. This ROM is based on CyanogenMod 10 (CM10) and is very stable enough to be used on your phone. This custom ROM will allow you to experience AOSP Android 4.1.2 with stock features and some extra features and customizations at system level. You can update T-Mobile Galaxy S3 SGH-T999 to Android 4.1.2 CM10 Jelly Bean custom firmware using the tutorial below.

As you continue reading below, we will guide you through the entire process of how to install Android 4.1.2 CM10 Jelly Bean on T-Mobile Galaxy S3 SGH-T999 with complete steps. Please make sure you backup all your data as given below because this tutorial will wipe your data. Remember, this is a custom ROM, not an official firmware update by Samsung. Let’s get to the tutorial now.

Disclaimer: All the tools, mods or ROMs mentioned below belong to their respective owners/developers. We ( or the developers are not to be held responsible if you damage or brick your device. We don’t have you on gun point to try out this tutorial 😉

NOTE: Since this is a nightly build, make sure you know that after installing this firmware update, your Android device can get FC errors, boot loops, several other bugs, apps might not work or worse, your phone might not boot. To fix, you will have to reinstall stock firmware or any other stable custom ROM.

UPDATE: CM10.1 with the latest Android 4.2.1 is now available for this Android phone. Read here for the tutorial.

Make sure you have installed all your USB drivers for the Samsung Galaxy S III to connect it with the computer. Download Samsung T-Mobile Galaxy S3 USB drivers! Apart from just the USB drivers, there are a few more things that you need to take care of.

1. You need to enable USB debugging mode. This helps to connect your Android phone with the PC. See here: How to Enable USB Debugging.

2. Your phone battery should be 80-85% charged. If your phone goes off suddenly because of battery, during flashing ROMs or installing mods and updates — your phone might go dead permanently. See here: How to Check Battery Percentage.

3. Backup all your important data that you might need as soon as your flash a new ROM, or make a backup for just in case, you never know when anything might go wrong. See below on how to backup data:

Data can also be backed up using Samsung KIES for their devices, but if you backup data manually, you get more options what top choose from and it is very easy to move data across Android devices from different manufacturers, i.e moving Samsung Galaxy Note backup data to HTC One X.

4. Your phone should be factory unlocked. Additional instructions for locked Android devices will be added in the tutorial for unlocking devices.

Now, let’s proceed with the tutorial on the next page and update T-Mobile Galaxy S3 SGH-T999 to Android 4.1.2 CM10 Jelly Bean custom firmware.