goTenna
Credit: Courtesy of goTenna

The goTenna turns your smartphone into a walkie talkie with a 50-mile radius, allowing you to send texts, maps, and emergency signals to others with a goTenna, even where there's no cell-service. The device pairs with your phone wirelessly via Bluetooth and while it's capable of reaching 50 miles over a flat surface, it will more realistically have a 2 to 4 mile range in the wilderness. The company claims a single charge lasts around three days and all the messages sent are private and encrypted. Designed for the backcountry, the goTenna comes complete with integrated offline maps.
[$149 for two; gotenna.com]