[Braxo]

Unfortunately I cannot remember when I had my iPhone 4.

My iPhone 4s (with iOS5) can stream Spotify to my speakers using an iPod's USB cable.

Sometimes, I'll have Spotify playing, then I plug in the USB and select it through my non-iDrive system. At this time, the music sometimes stops as my phone's Music app opens and begins to play. I have to manually go back to Spotify and start the song again. After that, it continues to play Spotify. Perhaps it would also help to close the Music app.