From the most heavily themed to the ones with a more stock look, you can find a wide selection of custom ROMs for your Android device in many Android Forums. When choosing a ROM to install, most of the time you have to weigh each ROM's features carefully. Some custom ROMs come with a lot of features but are very unstable. There are also those that are fine-trimmed for faster performance without the need to overclock.

Suited for T-Mobile Samsung Galaxy S3 users who price performance over features, the Slim Bean ROM puts the slim on your phone. As its name suggests, the ROM is based on Android 4.1.2 Jelly Bean without the unneeded apps. It's also fully compiled from AOSP source with some hand-picked features from two of the most well-known custom ROMs, CyanogenMod and AOKP. The Slim Bean ROM works great and is definitely a must-try for those who love slim and fast ROMs.

This guide shows you how to flash Slim Bean ROM for the T-Mobile Galaxy S3 T999.

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 model number SGH-T999with ClockworkMod Recovery installed. For help, check out our guide on how to flash ClockworkMod Touch Recovery 6.0 for the Galaxy S3 T999.
• Download the following:
  • Slim Bean ROM (Slim-d2att-3.1.0-OFFICIAL.zip, sha1sum: 6b8ed1e4b5e92ab136fd874877b0787e6ae760d5)
  • GApps (Slim_Gapps.zip, sha1sum: 0d0b16d1d2b2a9e82325b67caf0d52e180c45454)
• 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.
• Make sure that your phone's battery power is at least 50% to avoid interruption due to power loss that may cause damage to your phone.

Instructions

1. Copy Slim-d2att-3.1.0-OFFICIAL.zipand Slim_Gapps.zip to your phone's internal SD card.
2. Turn off your phone.
3. Boot the phone into ClockworkMod Recovery Mode by holding down the Volume Up, Power, and the Home buttons until the screen turns on.
   • Once in Recovery Mode, use the Volume keys to navigate through options and the Power button to select an option.
4. Create a NANDroid Backup. Go to Backup and Restore > Backup.
5. Select Wipe Data/ Factory Reset > Yes.
6. Select Wipe Cache Partition > Yes.
7. Select Advanced > Wipe Dalvik Cache > Yes.
8. Select Install ZIP from SD Card > Choose ZIP from SD Card > Locate and select Slim-d2att-3.1.0-OFFICIAL.zip > Yes.
9. Select Install ZIP from SD Card > Choose ZIP from SD Card > Locate and select the GApps package.
10. Select Go back > Reboot System Now.

Great job!  You've successfully flashed Slim Bean ROM to your T-Mobile Samsung Galaxy S3 SGH-T999.