从现有网站制作移动应用程序

I have already developed a fully-functioning website, and our team is looking to export this site to an iPhone application (and eventually other platforms). The best example I can give is I basically have made Facebook, now I want to make Facebook's app (the one that is launched from an iPhone's home screen, not from the browser). So, obviously, we already have the functionality, and we just need to convert it to another platform. How difficult is this? Will we have to make a completely new piece of software and basically ignore all of the existing PHP code that we already have? The app is basically going to be the same as the website, except for a few layout changes. We might want it to be able to access the camera feature and definitely be able to upload a picture, which I think would rule out a mobile application? I still don't understand the delineation between making a mobile application and an application that launches from the home screen of an iPhone. Do you guys have any suggestions as to where to start and how difficult this all will be? If we can get the functionality we want and make it easier on ourselves by using existing code, we would be thrilled.I have already developed a fully-functioning we