I use an ios app similar to this but it works over bluetooth. I use an iPod touch loaded with music connected via the aux input to my boat stereo and can select music and control volume on it remotely from my iPhone over bluetooth. I have been 200 ft away and still had control over my music.
Much better option, IMHO than streaming bluetooth because I don't need a strong signal to control the iPod and better than that, no compressed audio through my $2,500 audio setup. It's called Tango, I think it cost me like a buck or something. Very cool app.