There's a similar app designed for cruises, where you can talk peer-to-peer over the ship's wifi without actually being online. It could work if you have a wifi antenna with you.
Recently my wife and I had separate seats in an airplane and we didn't want to pay for texting. I thought about how I could set up my phone as a hotspot with a captive portal which just presents a chat interface. Nothing came of it, but it was something interesting to think about on a flight, at least.
