Is it somehow possible to change the format of a telephone number being displayed? On my Samsung Galaxy S phone a local telephone number is displayed in the format 999-999-999.

Is it possible to change this format ?

Our local numbers are normally displayed as 99-999-99-99 , certainly the first two numbers are the area code.

Maybe is has to do with my language settings, because I used English as language.
Try changing your language setting from "English (US)" to "English (UK)".