I was just reading a post by Hayden about an interesting service by Moodio. The service essentially lets you listen to most web radio feeds from the native RIM media player application. It just recodes them into low bitrate streams.
From what I can tell this is OS 4.5 only but it may work with OS 4.3. What you need to do to make it work is go to www.moodio.fm from your desktop and sign up. You then search and add radio streams to your profile. You then go to m.moodio.fm from your BlackBerry and sign in. Then just click on the radio station you wish to listen to from that site.
It worked for me on my 8310 on AT&T with OS 22.214.171.124 but worked much better on my 8330 from Sprint with OS 126.96.36.199 due to the EVDO speeds. If you need some help check out this thread on PinStack.
Done. Now if only Pandora would offer streaming radio for BlackBerry…