Hi there I've recently fitted an Audi RNS-E head unit and want to fit the Bluetooth unit so I can use my iphone phone through it. I've been looking on eBay and have seen that there seems to be several different part numbers, will any of the Bluetooth unit's work or do I need to match the part numbers? Also does the Bluetooth device allow me to play my MP3's from my phone as well? If it matters my car is a 2004 54reg A4. Thanks for any advice.