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2) Is BMW prewired for telephone. All North American BMW E39s are prewired for telephone, but some Euro and other Region BMW E39s may not be prewired for telephone. A quick check option is to look at the panel where the overhead lights and located and determine if you have the microphone trim piece.
Photo 1 No Microphone trim piece. - Car most likely NOT prewired for telephone
Photo 2 Prewired for telephone. Photo shows Panel removed with arrow pointing towards back side of microphone trim piece