E46 Bluetooth not working with iPhone 5?

[P Ride]

Hey, I have an E46 330CI M Sport, which has the standard BMW Business CD unit with bluetooth - I've also added an auxiliary lead to the rear, which I drilled into the ashtray area. Works great.

I've paired my Bluetooth unit with my iPhone 5. The iPhone can see the BMW unit and the BMW can scroll through my phone book, but when I take a call, it doesn't work through the BMW. No sound at all.

Any ideas?

Thanks