http://www.gotenna.com/pages/how-it-works
How goTenna works:
"goTenna enables you to communicate without any need for central connectivity whatsoever—no cell towers, no wifi, no satellites
—so when you're off-grid you can remain connected. In fact, goTenna will even work if your smartphone is in “Airplane Mode”!
How does this magic work?
Pair your smartphone to your goTenna device wirelessly, using Bluetooth-LE. Your goTenna needs to be within 20 feet of your phone,
so that the two can communicate with each other. Use our free app to type out a text message or share a location. Your smartphone
will send the message to your goTenna, which will then shoot it out, via long-range radio waves (151-154 MHz), to the intended goTenna(s)".
Only $149,99......!!
But that goes for 2 of them 
How goTenna works:
"goTenna enables you to communicate without any need for central connectivity whatsoever—no cell towers, no wifi, no satellites
—so when you're off-grid you can remain connected. In fact, goTenna will even work if your smartphone is in “Airplane Mode”!
How does this magic work?
Pair your smartphone to your goTenna device wirelessly, using Bluetooth-LE. Your goTenna needs to be within 20 feet of your phone,
so that the two can communicate with each other. Use our free app to type out a text message or share a location. Your smartphone
will send the message to your goTenna, which will then shoot it out, via long-range radio waves (151-154 MHz), to the intended goTenna(s)".
Only $149,99......!!
But that goes for 2 of them 
