The cell network that BMW assist uses is different than what normal cell carriers use. They utilize the radio frequencies uses by commercial vehicles and assure users that a connection is always possible. One of the features they offer is 5 critical calls. Meaning that if you don't have a connection with your normal cell phone, they can make a call for you through their network.
As far as tires, the fix a flat plus the small pump can get you enough range to get you to safety.
///2013 M5 Alpine White/Black,Orange County CA\\\