Great!!! So the M5 is done and you either were able to follow the manual instructions or wrote it down. I don't recall seeing in the telephone manual that if a phone stops pairing to delete it and start over. Make sure you note that if the manual does not. I have had a phone stop pairing and that was the only way I found to correct it. I assume the M5 asked for your iPhone passkey rather than the car's bluetooth passkey?

Is your wife's phone available to pair with the M5? Or can you try pairing either phone to the 2006 4.8?

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas