This tutorial will guide you on how to install CM10.1 M3 Android 4.2.2 Jelly Bean Custom ROM on T-Mobile Galaxy S3 SGH-T999. This process is quite similar to installing other custom ROMs however the only difference will be the files you use (obviously). In case you are a beginner, you have nothing to worry about because this is a comprehensive tutorial taking you through every single step involved. Before you being you need to ensure a battery life of at least 50%. You need the correct USB drivers installed in your computer and also ensure that USB Debugging Mode is enabled. Lastly, if you so wish, please backup your data because you will lose everything. If you are ready to proceed, please follow the guide after the break.