I have only had to use BMW Assist one time, and it did not work. The incident was in my Z4, not the X5, and was not an electrical issue -- there was no service available where I was?! So... Unlike OnStar, and possibly others, I think BMW uses the cellular network to speak with you. I had to use my cell phone (which did work) to call BMW Roadside Assistance and speak with a person.

-- Kelly