I just came across this post. I wanted to confirm for everyone that it works with the X3.
I was able to locate my vehicle (nearly useless thanks to BMW's 1km restriction) and use Google's send-to-car. I was unable to honk the horn, but I have heard you need a July 1 2014 production date or newer car for that work and my car is only June 27 2014.
Once they get the BMW Connected app working properly, it's "goodbye iPhone" for me.
http://f10.5post.com/forums/showthread.php?t=821663