If youve found a need to work with JSON (including with the iPhone), I want to point you to an excellent Google code project: http://code.google.com/p/json-framework/. The author of this framework can be found here.
This framework implements a strict JSON parser and generator in Objective-C. Its easy to work with and can be used across any number of projects with ease.
To use this framework it was pretty straightforward to get things in place, copy the included SDKs folder onto your local system (into ~/Library/SDKs). From within a project, modify the target build options to point to the SDK and add a link option to include the necessary library into the build.
From this point forward, the SDK is now available for use within any project, simply update the build settings and you are good to go.