The Top 10 iPhone passcodes were: 1234, 0000, 2580, 1111, 5555, 5683, 0852, 2222, 1212, 1998
Is yours listed? 🙂
A couple of things to note here, I think his sample size is probably large enough that the data is probably roughly applicable to Android and WP7 as well, not just limited to the behaviors of iPhone users themselves.
If you want just the analysis, head to the link above. If you want the backstory around how he collected this information, it starts with the Big Brother Camera app for the iPhone which reached #18 most popular iPhone application. Then leads to analysis of passcodes his app was sending back (not the screen unlock codes!), and eventually the back and forth with Apple as they removed his app.