iphone app using phonegap

I am creating an iphone app using phonegap. It utilizes java which im sort of getting my arms around. As i look at what I need my app to do, I realize that I need a db for users so that they can post things to a forum type thing. Hence, wordpress! So I’ve explored the json/ajax/xml blah blah blah. Im a designer by trade note a developer but have a decent understanding.

I have a working skeleton for my app using phonegap with the iphone sdk. What I am trying to figure out is, how to point a login from my app to my wordpress db so that I can utilize some of the functionality of word press in my app? I think that this problem might not be so difficult if I had a better understanding of json and all that. I have the json plugin on my site and see how to make it return values but am not sure how to translate that into my app.

I basically need to have a user login and begin a “session” in wordpress so that they can utilize the tools in the app. Any help would be much appreciated. this is a grad school project and Im starting to fear that I may have bitten off more than I can chew. Thanks in advance for any help.