Your iPhone is essentially a little computer in your pocket, and just like a computer it could suffer from the occasional freeze. Unfreezing the phone usually requires a soft reset, performed by pressing the Power and Home keys until the Apple logo appears. Solving the freezing problem depends on what's causing it in the first place.

Causes

Like your desktop computer, your iPhone needs the most up-to-date software installed to operate properly. If you haven't updated your iOS recently, it could be causing your phone to freeze. Low internal memory can also affect performance, resulting in unpredictable behavior. A corrupted or faulty app or program could be the culprit, especially if your phone freezes when you try to use the software. Finally, the phone can overheat and lock up if is under blankets, in a hot car or otherwise outside of its recommended operational temperature range.

Solutions

Ensure you're using the most current version of your iOS by tapping “Settings,” “General” and then “Software Update,” or connect through iTunes to update through your computer. If the freezing started after downloading a new app or program, uninstall the program and see if the problem continues. Delete unused photos or videos from your phone to ensure plenty of free memory space to prevent operational problems. If your phone has locked up due to overheating, the problem will usually solve itself if you move the iPhone to a cooler place.