Hi M. I don't have one but my boss does. Yeah you can stream music through BT.
I have an iPhone 4 and it works fine and it did with the 3GS, but the quality is noticeably worse than wired through the 3.5mm jack. Imo the sd functionality is best. Just get a 16gb card for £20 ish and keep all your music on that and not have to keep unplugging.
I really want one but be careful because halfords don't include the wiring harness in their £200 deal.
The harness will be about an extra £20. Have a google because I've seen one for about £140.
Not sure about fitting but I've seen lots of stuff on here about ripping the headunit out.
I'm definitely getting an mki9200 soon so I'll keep you informed pal.
Hope this helps pal.