json webservice from iphone/ipad
The canonical JSON processing library is here, and was written by the Stig Brautaset. Stig's around SO and occasionally pops into obj-c-json discussions.
Check this out. Shows JSON used with Flickr API's on a native app:
http://iosdevelopertips.com/networking/iphone-json-flickr-tutorial-part-1.html
Its a 3 part tutorial and links to the other parts are seen as you scroll to the bottom in the above link. They also have general JSON framework tutorials as well in two parts. Links again can be found in the above page itself. Very useful and pretty much helped me complete all the JSON stuff in my app. Project code is also available for download.