3 things you must have in mind while making your application scalable.

If your application is scala then you allow your application to support the different display sizes, resolutions, and layouts for different S60 devices.

1. Layout information should not be hard-coded.
The S60 platform provides the AknLayoutUtils class for building layouts from resource files.
Note: that you need to override CCoeControl::HandleResourceChange and CEikAppUi::HandleResourceChangeL in your application to draw your application again in the event that the orientation of the display changes.
2. Scalable fonts should be used.
The S60 platform provides methods in the AknLayoutUtils for using logical fonts from an enumeration in the avkon.hrh file.
3. Scalable icons should be used.
Scalable icons are based on SVG Tiny (SVG-T) format graphics.