This is peer-to-peer networking for the backcountry. The goTenna Mesh overcomes the inability to send text messages with your smartphone when you’re off the grid and can’t connect to mobile signal towers.
They are sold in pairs, so you can communicated with other people in party through your smartphones when separated (if they also have one of the devices). You can send private messages between two phones or to a group group of people.
If other users (outside of your party) are nearby their antennas will boost your signal for further range, so the more users in the vicinity the better the range.
The devices work on both iOS and Android devices. A pair sells for $200 and are available for preorder.
This video does a good job of explaining how the devices work: