HTC Evo 3D received the Android 2.3.4 software update today which brought several fixes and the long-waited native screenshot capabilities.
You can now take screenshot natively on your HTC Evo 3D with the shortcut: Power + Home button. You keep on holding the power button and quickly tap the Home key. You screenshot will be saved to the Camera roll.
This was included in the Android 2.3.4 software update for HTC Evo 3D.