Answers are in this thread:
It looks like a 2008 probably does not have this capability and certainly doesn't without iDrive. But for a few dollars, you can buy an aftermarket device that will let you do it.
128i Convertible, MT, Alpine White, Black Top, Taupe Leatherette, Walnut, Sport
Ordered 5/22/09, Completed 6/4/09, At Port 6/9/09, On the Georgia Highway 6/13/09, Ship Arrived Charleston 6/24/09 at 10pm, PCD 7/21/09