I have an Galaxy Attain 4G (SCH-R920) on MetroPCS running the Android™ 2.3 (Gingerbread).
How can I root this phone?
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A step by step tutorial accredit to Zhelezaka from http://forum.x-drivers.com/.
Necessary Files: all files hosted on my DropBox account!
Download all files from the "Necessary Files List" to a folder on your desktop;
Extract odin3_v1.85.zip to a folder on your desktop;
Locate and open the Odin 1.85.exe to open up Odin3;
If the User Account Control (UAC) pops up, accept the execution of the file.
Click on the PDA button.
Navigate to the location where you downloaded the Attain-Rooted-Update.tar file and select it.
Click on the PIT button.
Navigate to the location where you downloaded the Attain-4G.pit file and select it.
Do not forget to extract the file first, since the application only works with the Attain-4G.pit file inside the ZIP you've downloaded.
Make sure that repartition is unchecked.
This is important as checking this will most definitely brick your device!
Note that when you select the PIT file, it gets checked, you need to uncheck it yourself.
Power down your device;
With your device switched off, press and hold the Volume Down + Home + Power buttons.
Then press the Volume Up key to enter the Download Mode.
Connect your device to the Windows PC.
You should see the ID:COM field light up yellow when you do this;
If this does not happen, it means that you don’t have the necessary drivers installed.
You can download Samsung Kies and install it to rectify this problem.
Your Odin3 screen should now look like the picture posted below. Again, make sure that the Re-Partition tickbox is unchecked before you click Start!
Click on Start.
Note: Once Odin3 says "PASS" and your device reboots, your Samsung Galaxy Attain 4G should be rooted!!
If you are in doubt though, the usual way to confirm is to download Root Checker from the Google Play Store or look for the Superuser app in the app drawer.