Want to root your AT&T Galaxy S2 SGH-i777 on ICS? If you have Android 4.0.3, 4.0.4, or any of the 4.0.X series, here’s how to root your phone easily using ODIN and Siyah kernel.
By installing Siyah kernel with ODIN, you will get root, Superuser, overclock your phone up to 1.6Ghz (with overclocking app like SetCPU), dual-boot multiple ROMs, and a whole lot more.
Step 1. First connect a micro-USB cable from your computer to your AT&T Galaxy S2 and hold down the Volume Up, Volume Down, and the Power buttons together for about 10 seconds.
Step 2. When you see the warning sign hit Volume Up button to enter the ODIN Download mode.
Step 3. Download ODIN and Siyah kernel tar file below and unzip the ODIN zip file but LEAVE Siyah kernel in .tar file format.