Cell Phone Abilities without Cell Phone Tower

Hi All, I'm not sure where to post this.

I like to drive in the mountains with friends, and we are constantly on the phone, evaluating the cars we are driving, talking about the handling, engine, engine sound, etc. We love cars.

When doing this we typically talk on the phone, however sometimes there is no reception and we can't talk.

Does anyone know a way to talk with privacy between the cars, without a cell phone tower as the mediator? If would be awesome if the phones could connect between each other.

I thought of walkie talkies, but I don't like how other people can listen in and interrupt into the conversation. Even if we used privacy codes, people can still hear they just can't interrupt without the same code. I've heard that some people can even still find the code an interrupt.

Again, ideally, something with cell phone abilities direct from cell phone to cell phone within a reasonable range, without needing a cell phone tower would be the ideal thing I am looking for.