The first requirements if you want flashing Ice Cream Sandwich custom ROM on your Sprint HTC Evo 3D CDMA is Gaining root access. There’s two type of rooting Temp Root and Full Root, in order to install a custom ROM you should make your HTC Evo 3D has Full Root access with S-OFF. All brand new HTC android smartphone or tablet come with S-ON which mean you can’t modify system area, that’s why you need to change it to S-OFF this will make system partition (NAND) unlocked and get Full Root access.
How do I know if my Evo 3D CDMA is Unlocked (S-OFF) ?
You need to boot into bootloader by turn off your phone and then hold down the volume button while pressing the power button until the white screen appears. Take a look at the top line, you will discover S-ON or S-OFF status there, still on the bootloader screen you can also find the Hboot version of your Sprint Evo 3D. If your Hboot version is 1.40 or below you can use Revolutionary Tools to get S-OFF, but if your phone has Hboot version 1.50 you need to utilize HTC Unlock method.
For those who want backup all apps and data on their Evo 3D android smartphone before performing a full root process, you can follow the video tutorial below by thedroiddemos.
How to Full Root HTC Evo 3D CDMA on Hboot version 1.30, 1.40, or 1.50
As described previously that root method depends on Hboot version. For Hboot version 1.40 and below you can follow the guide and video tutorial by thedroiddemos.
If you has the latest Hboot version 1.50 you can follow HTC’s unlock method, this method will leave your Evo 3D S-ON but you can still flash any ROM on it. You can find the tutorial and video on xda-devs thread. So, if you have a good luck with rooting process on your Evo 3D you can continue with installing any ROM including Android 4.0 ICS ROM.