4s phone screen is frozen
Sometimes the homescreen seems to hang on iOS7.  Sliding up for the camera, or down for notifications centre etc can work, but sliding across to unlock doesn't.  It's very annoying.  You need to restart the phone to get past it.  You can either:


hold the power button until the slide to restart message appears, and if you can slide there then do that, or...
hold the power button and home buttons together until the Apple logo is shown.