One of my personal favorite bands, The 88 [iTunes Store], recently recorded an entire single using nothing but an iPhone and their instruments. The app they used is called FourTrack [our review] and the song is called "Love Is the Thing" [iTunes]. We could honestly go on and on about how cool it is that they published a song recorded entirely on the iPhone to iTunes, but it may be more succinctly explained in the video below. Enjoy!
