Make sure you leave Darwin or the Alice with a satellite phone. You can lose mobile access less than an hour or so out these places!
If you work in the Territory or you are in the 4WD heading to Kakadu, Litchfield or Nitmiluk national parks or further afield then a satellite phone could save your life. If fishing is your passion in the Daly River chasing Barra or heading out to the islands then help can be a long time away.
Australia has only 27% mobile coverage so don't count on your mobile phone in the Northern Territory!