The iPhoneWebDev is providing a discussion forum for developing applications for the iPhone. They refer to portable Web 2.0 applications. I have asked the forum if someone with a phone can try the Sahana disaster management system. The iPhone has a bigger screen than many other smartphones so may be useful for use by emergency workers (assuming it is robust enough).
Also Tom Yager has suggested using email to get around the lack of an accessible file storage on the iPhone. You email the data to the phone as an attachment and then the appropriate application can access it. Of course if you used something like the Open Moko Neo1973 Smartphone you would have the Linux file system available.
There was also an iPhone Developer Camp recently in the USA. But I would not want to become locked into developing applications just for the iPhone. I have provided some general tips on how to adapt web applications for smartphones, including the iPhone. The idea here is to avoid having to build web applications just for the phones and instead make pages for desktop screens compatible.
In several years of teaching web design I have seen many proposals for hand held web businesses come and go. So far few outside Japan and some other Asian countries, have
managed to make money from mobile data.