Music streaming requires A2DP bluetooth compatibility, which MINI did not see fit to add to their stereos. I have an '08 JCW
with Boost and phone bluetooth, my sister has a 62 (2012) ONE with visual boost and phone bluetooth. Neither support A2DP, so we both bought Y-cables to use with our iPhone 4 and 4S respectively.
It's annoying that you have to plug in to listen to music but in fairness I'd always plug my phone in anyway, as the battery needs charging so often!