I have an app that runs slowly on an iPhone 3G but is fast enough on an iPhone 3G S.
Is there a way to limit the app to be available only for iPhone 3G S and faster
You can set minimum capabilities required to use your application by providing values for the UIRequiredDeviceCapabilities
key in your application's Info.plist. In this case, I'd recommend using the opengles-2
capability, because all iOS devices with the post-iPhone 3G S faster hardware support OpenGL ES 2.0 and none of the ones before that do.
For more on these capabilities see Apple's documentation here.