Thinking out of the box...if you're only concerned about backing into your garage and you want to use your I-Phone...you could mount a camera in your garage and access it via your I-Phone's internet connection. You'll have to deal with some lag in the system but you wouldn't have to install anything on the car.
2010 E93 335i M LeMans Blue
2001 E 46 330ci Coupe/silver/black/Sunroof
1999 BMW R1200C Cruiser-Ivory & Blue