Zello

[Joe]

That's true Lightspeed, it's pretty much a data service on the mobile phone network but it works pretty well for low level event.
I use Zello all the time, I have an old mobile phone sitting in the living room and it's just another comms channel, no Sim required as it's through the WiFi. I can even use it to talk to dogs when I'm out.

Skean you should give it a go, it takes about ten minutes to work out the basics and it's very handy if your out hunting or doing other outdoor sports that need some sort of comms. Plus it takes a few minutes to set up group chats.