I had already tried searching. I'd found some retrofit bits. Unfortunately basic things like what the steering wheel controls do are lacking. Like my searching of the cdv.... that took a while to find out what that actually did. Though lots of threads saying remove it and how to. And I know no longer whether it's cheapest to buy a M steering wheel with MF controls from BMW to get this, or whether things have changed and just buy the controls etc. as times move on.
You are right there is little info available about the functions of the controls and I did have to ask when I fitted mine.
All I can tell you is that you can change the volume on one side and the radio channels and cd tracks on the other.
There are two other buttons one on each side which are related to the use bluetooth I believe, which I do not have so was irrelevant to me but I'm sure someone will throw some light on the question shortly.
The R/T button switches between the telephone function and general radio/CD/NAV or whatever is currently displayed on the nav screen. The face button is to pickup or drop a call.
Thing is you can have multifunction buttons on the skinny wheel and the chunky wheel, but most people tend to upgrade not just to obtain multifunction buttons but more for the better feeling chunky steering wheel.