I'm doing something similar for local news/events, called SeeAround.me, where people can see/submit local news stories and their locations. But I could see sort of a cross between that and Your Audio Tour as particular interesting for people who want to do their own walking tours, for example.
I already made that for a client. Don't think users will write stories from their mobile, at least good ones. It was difficult to start with no content, too similar to twitter.
