Why no mobile phones?
Wby did not one character had a mobile phone on them in the movie?
The greatest trick the Devil has ever pulled was convincing the world he didn't exist!
Pete is seen with a mobile phone in the pub at the beginning and the reception is not good.
I think you have to accept that a lot of the phones were lost/damaged with the other equipment when the boat is holed.
Believe you me if you know anything of the Northern Territory, there would be almost zilch chance of coverage deep in those gorges.
What was more unlikely IMO was the radio message not getting through.