The iPhone/iPod Touch version builds on the strong foundations laid down by the GP2X version by adding an automatic save system, reengineered controls, HUD refinements and further gameplay improvement.
Probably the most important part of any game is the controls - if these don't work well then the game would be about as useful as a chocolate teapot. For this reason, getting the controls right was the #1 priority in the iPhone/iPod Touch version of Payback. We tried to keep the on-screen buttons as minimal as possible so that they did not distract from the gameplay itself.
The game uses transparent up and down arrows on the right of the touchscreen to move forwards and backwards. The steering is handled using the accelerometer (tilting left and right) and there is a wheel displayed to show how far you have turned. This version doesn't support multiplayer but at only 6.99 USD / 5.49 EUR / 3.99 GBP, it's still great value as a singleplayer game.
There are more screenshots and details here: Payback iPhone report