This app was mentioned in 3 comments, with an average of 1.67 upvotes
No problem! The app that I used was Bluetooth Chat, and it worked well for me. I would suggest testing it out with a few devices beforehand so that you can all connect in-flight without issue.
I have few solar charges for usb systems so I can have my phone up and running at least once every five days.
It's just a push to talk phone that can adjust radio frequency. A friend of mine help me find the right one and it's been working pretty well.
This guy has something similar but mines was a larger flip phone (need to switch to past tense as I long since turned it over when I left security it was a company phone).
https://www.youtube.com/watch?v=94psaZvJ2UI
Here are some push to talk phones. I don't know if these require a phone plan to all work.
There are similar apps that are free and use a antenna or headphones to do radio stuff.
The bluetooth is a lot easier to explain. Just download this and turn on bluetooth for your smart phone.
https://play.google.com/store/apps/details?id=org.jastrzab.serwer.bluetooth&hl=en