Ask YC: How to turn my website into iphone app?

Hi guys. I run a social networking site. I am thinking about writing a iphone app that lets people log in to send/receive messages to their friends. So basically all this capability is available from the website. I would like to write a iphone application to do the same. I know I can use the iPhone SDK to create an application but what I am not sure about is how to let that application connect to my site. Do I just write some php pages that return xmlrpc data that my application then just parses to display? So meaning that the iPhone app will call a 'web url' .. make a request.. get back some xml data and then display that? Is that the general idea??

Thanks!