While I don't have an iPhone, I know it's wifi capable which makes it usable without having to use data minutes (again, I'm not a user so I don't know the costs)..you can log into a local wifi network and you're good..the problem then might be audio quality. I know plenty of stations that use lower bandwidth bit-streams which is like listening to AM radio, imho.
And then you get to listen to the web advertisements...which tend to lack in variety so hearing the same local PSA or ad for a local jeweler several times (sometimes in a row) over the course of an hour might make one quickly jump to a new source.
But correct me if I'm wrong, after looking at the Flycast site, the listings of radio stations they offer seem to be limited in some cities and in all honesty, it looks like the list of radio stations on iTunes. I'm not knocking the app, I'm sure it's a great source..but so is Slacker...I'm just skeptical that this would be that much of a challenge for satellite radio. Not everyone has iphones or wifi capable phones (there's a couple of wireless carriers that like to nickle and dime subscribers for anything and everything...free wifi will not be on their agenda as long as they can continue to charge for web access). Maybe if the new FCC chair moves forward with the nationwide wifi, that might change.