I have the iPhone NatureSpace and ThunderGod (!) apps, but they only play the audio so long as you have the app open.  I was thinking about purchasing 1 or more of the albums available in iTunes so that I can listen while I do something else, but am holding off until after the holidays JUST IN CASE THEY END UP UNDER A TREE OR NEXT TO A MENORAH OR SOMETHING LIKE THAT.

Thus concludes another lesson from the Marc Goldberg school of subtlety.