My iPhone app will call a JSON Api to load text and images. I've seen some JSON frameworks like http://iosdevelopertips.com/cocoa/json-framework-for-iphone-part-2.html
How to fetch and parse JSON in an iOS App?
I find that the best way to do it is indeed by using json-framework for json parsing and generation, and ASIHTTPRequest for the http communications.
This is my setup, and it's wonderfully simple to work with.