Like Stangmatt66 said, some early production X3's did not have the white connector properly wired to the sharkfin antenna. There was a service bulletin on this so BMW will fix it without problem. My X3 was produced in December and it was properly connected (did a self Sirius install as well).

The antenna connector with the white plug removed (and before installing the curry connector) can actually connect to a regular Sirius satellite (or even XM) radio so that would be a way to test if you actually had the means - but that is sort of a hassel.