The question is a bit too vague. With the N900 you can do what a normal computer would be able to do. So the question you're asking is: are there any security holes in the galaxy S that are exploitable over a network? For that, I would ask in an appropriate forum. THEN, once you know which hole you want to exploit, and (possibly) which tool(s) you'd need, you can ask again here (or find/compile the tools yourself).