A smartphone has a 500 mw antenna, has a rather limited battery capacity, and is prone to worse than optimal reception inside a steel/windowed car.
A BMW with this tech uses the roof-mounted 2000 mw antenna, has a rather big battery capacity, and provides the best reception you can get.
If you're happy with your wife and kids watching Internet video's over your Iphone 5 connection, that's fine. But don't say this tech/option from BMW is useless.
Kids: want to stay in the car, and play, while daddy is shopping for just 15 minutes
You: Want to take your cell phone with you, because you want to be reachable.
Kids: now don't have Internet connection anymore...
You: Reflecting "Damn, BMW was right about offering this option after all..."