[joshmarinacci]

Not really. This stuff is heavily NDA and patent encumbered. You’d be better off setting up a local wifi network and using an IP based audio call system.

[seidleroni]

I'm not sure if this applies to all carriers but with many carriers if you are on wifi you can send/receive text messages and sometimes even make calls. Certainly you could use WhatsApp or similar in that case.

[mikestew]

...with many carriers if you are on wifi you can send/receive text messages...

How would you propose that those messages get routed if there is no connection to either the internet nor a cell provider?

[pavel_lishin]

Not if I'm in the middle of the woods with no connection to the outside world.