You need to confirm the spec of your car with the dealer, namely that it has option SA640 "Car Telephone Preparation", otherwise you'll need to get wiring. I can't give you the part numbers for an E53, but if you read this thread of mine for an E46 it will give you a pretty good idea of what is needed. You can do it for much cheaper than $1700

Car Telephone preparation - What does it entail? - MTorque - Passion for M