The pre and 09 cars came with pre wiring for a lot of stuff and even the Hi Fi has a fiber optic line run to the trunk for a cd changer. The fiber optic loop is used to add the blue tooth phone module , satellite radio and bmw assist.( Even in the Hi Fi)
See the electrical and entertainment system pdf
Only the newer BMW's may not have a Most Bus from what I read.
There are a bunch more technical pdf's here