How can I scroll in a text box on the iPhone?

When browsing the web in Mobile Safari, scrolling up and down is pretty simple. One finger will drag the whole page up or down to reveal the rest of the web page. The problem is that text boxes within web pages don't show scroll bars.

To scroll within the text area drag two fingers inside the text box instead of one. This will result in the text area scrolling in the direction you swipe, while the web page remains still.