I use a Garmin 255W in my 2008 E61. I mounted the black metal disc that comes with the unit near the right front corner of the flat plastic panel in front of the i-drive screen. The suction cup on the mounting bracket adheres very securely to the metal disc, and the disc is fairly unobtrusive when the bracket is removed. However, I generally leave the bracket in place as it does not block the screen and is not visible from outside the car. The Garmin screen is at the same level as the i-drive screen, but does not interfere with the driver's view, although it does block some of the screen for the passenger. The unit is plugged into the outlet in the footwell, and I store it in the mesh pocket in the footwell, where it is easily accessible, but again not visible from outside. While certainly not like a built-in, this works very well for me.