I suggest using the excellent ASIHTTPRequest source from All-Seeing Interactive: http://allseeing-i.com/ASIHTTPRequest . I do this, and so are a few released iPhone apps, so you can be sure that the code is pretty strong.
This is the CFNetwork API wrapper that simplifies some of the more tedious aspects of interacting with web servers. It is written in Objective-C and works in both Mac OS X and iPhone applications.
It is suitable for making basic HTTP requests and interacting with REST-based services (GET / POST / PUT / DELETE). The ASIFormDataRequest subclass simplifies sending data and POST files using multipart / form-data.
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