what you're going to end up doing is pressing and holding both the volume up and the Sleep/Wake buttons again. However, you're first going to effectively tell the iPhone that you want to restart instead of shut down.
Shift-Command-Option-Escape. If you instead press that, you don't call up this dialog box, you just force quit whatever application is in the foreground at the time. That is, it kills the app whose name is up next to the Apple menu in the menubar, and it does so right away. ...