Having a big conceptual problem here with the iphone input.

Example has been simplified.

I have a game. During one phase of the game tapping on the screen does something completely different then during the other phase.

So I basically have made two different classes that handle input logic and I want them to switch depending on the phase of the game.

I though of using notifications, but I hear that they are heavy weight. How do people typically do this sort of thing?