I'm having a similar problem. My iPhone 5 never would freeze before, but since I updated to iOS 7, it freezes about 1-2 times a day.
For me, it always freezes on the lock screen, while I slide to unlock. Usually before I enter my code. The screen freezes, goes black, then my iPhone doesn't respond to any buttons being pressed. The only way to fix it is to for me to restart my iPhone, by pressing and holding the two buttons for about ten seconds.
I have been trying to slide to unlock fairly slowly, which I think might help it not to freeze. It seems more likely to freeze when I slide to unlock super fast.
I love the new iOS 7 otherwise, so I hope this is fixed soon!