Apple has deigned to allow apps that use your iPhone 4’s LED flash as a torch into the App Store. Some cost money, others do not. Some are well-designed, some not so much. But they all pretty much work.
Turning your iPhone into a little LED torch will undoubtedly be handy at some point. If you just want to be sure you have something to turn that flash on when the power goes out, LED Torch Light should suit you fine. If you want one that’s pretty to look at, too, check out Ultimate Flashlight or one of the many other $1.19 options. [Actual LED Flashlight, Ultimate Flashlight, LED Torch Light]