Hold the home and power button at the same time. Ignore the slide to power off. Wait till you see the Apple boot logo and release both buttons. Wait about a minute and when your phone returns to normal try downloading the app again.
I've tried the reset and tired downloading again but when the app comes up it says waiting and the little loading wheel that's comes up by the 3G doesn't come up and the app stays dark and says waiting up under it. Got anymore ideas?