Don't count on it. "There are tons of dead zones — even in big cities — where there is no reception at all," says personal security expert Robert Siciliano. If you do manage to call the cops, it'll still take 10 to 30 minutes for police to find you because you're not at a specific address.
http://www.cosmopolitan.com/print-this/12-Rules-You-Should-Completely-Ignore?page=all