See It Now ($0.99) by Avocado Hills is a utility app that allows your iPhone 4 (or 4S) to magnify small text that would otherwise have been a problem to see.
The app features a digital zoom and allows you to turn on the iPhone’s LED light, which is almost always necessary, since the image is very unfocused without it. Even with the light, the image often shifts focus.
There seems to be no attempt at stabilizing the image. This makes it very sensitive to movement and impractical for extended reading such as with a book. Zooming makes it even worse.
However, for brief assistance with your vision, it can be very helpful. An example would be reading an ingredients list while out shopping. You’ll just have to be patient with the inconsistent camera focus.
Unfortunately, See It Now does not work with the iPhone 3GS.