It looks like new smart phone apps will soon be changing the way we listen to music.
Pandora, Slacker, Shoutcast, etc. are examples of customized, interactive radio for your cell phones that we will be seeing more of. These stations keep your music selection up-to-date, introducing you to new artists. and allow you to tailor your listening experience. They'll also most likely have your mp3 player collecting dust, while you instead grab for your cell.
Check out the article from Wired:
http://blog.wired.com/business/2009/01/six-ways-cellph.html