I was actually told that a magnetic clip can have adverse effects, in that it has the opposite effect of putting the phone asleep like BB. From what I've been told, there is a magnet in the car mount that's used for the GPS directions. The magnet actually wakes the phone up and and keeps the screen on. Can be a killer on battery life. That said, if you just have a holster with a magnetic closure that's not very strong, it may not wake up the screen. Just something to bear in mind.