When designing S60 applications, it's important to be follow S60 UI style. Users will find it easier to learn how to use your application, if the look and feel is similar to system applications. What comes to soft keys, in S60 devices the soft key labels are
- left soft key: positive actions like OK, Select, Options
- right soft key: negative actions like Back, Cancel, Quit, Exit
"Done", even though it can be considered as a positive action, can be placed to right soft key in forms, which have Options menu available (left soft key is "Options").
With E90 one should notice that on the PDA side soft keys are reversed compared to other S60 devices.
It should be easy for the user to close the application. The Options menu should always have "Exit" as the last item in the menu. Exit can be placed to the right soft key when there is no need for other labels and it's expected that user might want to close the application. In S60 3rd Edition devices pressing the End call key (Red key) closes the application automatically.