While touchscreens are generally intuitive to use, and there are a lot of casual games for iOS and Android designed with touchscreens in mind, most 'hardcore' games on those smartphone platforms still rely on virtual D-pads and on-screen buttons to emulate a traditional gamepad. This is problematic since touching the screen will invariably result in obscuring the view.
But it is possible to use a PS3 controller for playing games on Android handsets.
The PC classic GTA III was especially problematic. The game was recently released for Android and iOS, doesn't utilize the touchscreen effectively and thus suffers from this problem. This has prompted members of the xda-developers forum to find a solution on how to use a PS3 controller to control this Android game. Basically, it involves purchasing an app from the Android Market which will pair the Sixaxis controller of the PlayStation 3 with your Android device using Bluetooth. It then maps each button on the controller to an area on the touchscreen (as you can see in the picture above). That is, you will still see all the on-screen controls, but won't need to touch them anymore.
Considering that each game uses a different layout, it requires a lot of work to map the PS3 controller buttons to touchscreen locations. Said forum members have provided a guide with pre-made profiles for many popular games, including GTA III, Asphalt 6, Modern Combat 3, Real Football 2011, and Real Reacing 2.
To use a PS3 controller for playing those games on your Android device, follow this tutorial.