I just recently came off a fun little experience involving my first generation iPhone where the touch screen became unresponsive on the top and bottom rows. The cause is unknown but I talked to a wide variety of Apple and AT&T representatives to get some guidance with the issue.
Let me first and foremost stress the importance of getting the two year AppleCare Plan when you purchase your iPhone. Even if you already have yours it does not hurt to pick it up. You also want to make sure that at the very first hint of possible problems to notify Apple. There are also several accessories to help protect your iPhone from damages.
Here I'll describe a few procedures to take to try and fix the problem as well as what to do if you need to ship off the phone for repair. If an app has frozen up on your iPhone, it can sometimes be easily cured by using the Home button to unfreeze your iPhone without taking any additional steps.