While leveraging your previous code requires porting due to the new physical characteristics of the 5th Edition devices, you can still build on your previous S60 experience.
The main difference in user experience between S60 3rd Edition and 5th Edition devices is the user interaction model of touch, tactile feedback, and sensors. For more information on the user interaction model in S60 5th Edition devices, see Designing applications for S60 5th Edition.
In Touch UI, the device screen is sensitive to the user's finger and the device stylus, which replace the physical keys of the device as the main navigation and software manipulation methods. This kind of UI enables a variety of design possibilities that are impractical in traditional keypad-based mobile applications.
S60 5th Edition devices use resistive rather than capacitive input. This means that the UI is not only designed for finger input, but rather you get more precise input from stylus.
The UI is focus driven and not based on direct manipulation. This means the model is that first you select a control on the device, and then activate it. In order to maintain a consistent user experience, it is recommended that you do not to change UI components derived from S60 UI components to be directly manipulated.
Since the UI is focus driven, most of the UI components can be used in both touch and non-touch devices. For the exceptions and design considerations, see Designing application UIs for touch and non-touch devices.