Check out these tips. The article talks about iPad, but they work on iPhone too, even an old 3G.
One one hand, it shows the intense amount of careful thought Apple puts into the user experience. But on the other hand, it highlights the discovery problem. I know people who have been using iOS since before it was called iOS, and still didn’t know about these. How do you put these kinds of finishing touches into a product and make sure the target audience can find out about them? -m