not sure if this will help but i thought i would suggest what i have setup
My setup is quiet cheap and works well, i'll explain.
I bought like a cheap car radio that took headphone jack in front, cost me around 20-30 at the time, which you can get on ebay.
I use a program called audiogalaxy which streams over 3g, all my music over the web, but u do require to have your pc on at home all times,
http://www.audiogalaxy.com/I like this program because i dont have to upload or download any music onto my iphone and my collection of music is huge.
but you can also use this service which amazon offers, but you would need to stream the music
http://www.amazon.com/gp/help/customer/display.html/?nodeId=200593730There is a another service you can use when it comes out in the UK, which is google music
http://music.google.com