| BT will allow you to use buttons on steering weel to make and answer phone calls;
Dial numbers from a phone book;
Dial phone numbers by speaking them, rather then pushing keys;
Display incomming call numbers and outgoing numbers on your radio display screen.
And, yes, it does uses your car audio system...
Functions are dependant on your phone capabilities.
In the beginning of the year BMW was saying you have to have car made after 03/2002 to be able to to install OEM BT module, It could of changed by now | 
