Q:

Developing native applications to run both on Android & iPhone? 

I'm new to mobile phones development, but I wonder whether there is any way to develop native apps (HTML-based apps is another story) that would run both on Android and iPhone?  I know that there exist applications available for both OSs, so I wonder how are they ported/developed for both targets? 

A:

You can simply have two different projects, with same design and graphics, or, you can do it with some frameworks like PhoneGap or Rhomobile. 
The best way is to have two different versions of the code, so you can take advantage from the platform that you are using.