Is it possible to know the keywords used in AppStore for a given iPhone App? I would like to know if there is a way to find out the keywords used by an App when they submitted the app to the AppStore?
Unfortunately no: if you didn't submit it yourself there's no access to the keywords. They don't show up in the official RSS feeds nor in the scrape-able web pages. Searches in iTunes on a computer or mobile device are performed entirely on Apple's servers, so the keywords aren't exposed on the clients.