Android 5.1.1 started rolling out for Nexus device few days ago and kudos to developers, they had already prepared CM12.1 Android 5.1.1 Lollipop custom ROM for T-Mobile Galaxy S3 T999. When it comes to custom ROMs, people look towards team behind Cyanogen Mods as they release the best ROMs which are based on Stock Android and have great performance.
If you are ready to install CM12.1 Android 5.1.1 Lollipop custom ROM on your T-Mobile Galaxy S3 T999, then wait no further and follow the tutorial. However let me clear it to your that this is not official firmware update from Samsung nor T-Mobile, rather it is a custom ROM developer by some Android masters for your phone. Meanwhile according to testers, this ROM is bug free and can be used as daily driver.
- First of all, make sure your T-Mobile Galaxy S3 T999 is fully charged.
- Keep backup of all your important data.
- Enable USB Debudding on your phone.
- Download Latest Galaxy S3 Drivers and install them on your Computer.
How to Update T-Mobile Galaxy S3 T999 to Android 5.1.1 Lollipop via CM12.1 (Alpha) Custom ROM
Step 1: Download the CM12.1 Android 5.1.1 Lollipop Custom ROM and GAPPS for your T-Mobile Galaxy S3 T999 using above links and place the zip files on desktop.
Step 2: Connect your T-Mobile Galaxy S3 T999 to your computer and transfer the download zip files to your phone SD card.
Step 3: Turn Off your phone and boot it to recovery mode.
Step 4: In recovery mode, first tap on “wipe data factory reset” option to perform a factory reset. Once this is completed, go to advanced options and select “wipe the cache” followed by “dalvik cache” options to clear the cache.
Step 5: Go back to main recovery menu and select “Install zip from sd card” followed by “choose zip from SD card” and select the ROM zip file you have transferred to SD card earlier.
Step 6: Once custom ROM is flashed, use the same step (# 5) to install Google Apps you have download and transferred to your mobile earlier with ROM.
Step 7: Once the installation is completed, go back to main recovery menu and reboot your phone which might take few extra minutes for first reboot.