Re: Visiting in summer... eeerrr winter that is (WA, NT)
Top Red Centre is very steep but worth it. Plan on around 2 hours to do it. If you plan on going to Flynns grave or Simpsons Gap then Gillen is on the way it will take around 2-3 hours round trip depending on your fitness level (just to brag a little it usually takes me around 1.5 hours).
Cell phones pretty much do not work from about 40km out of Alice. Spotty around Hermansberg. Kings Canyon and the Rock are good but in between is also no go. HF will work or you can rent a Sat phone for around $20.00 per day.
Roos aren't garanteed, BUT, if you go to the Heavy Tree Gap motel at around 4-5pm you can purchase pellets and feed wild wallabies. It is actually more fun than one would imagine.
Usually around the Telegraph Station trig beacon there are a few hanging out in the afternoons.
Suprisingly enough Mereenie can be pretty busy, the one time we did it we saw about 10 cars, watch out for camels they're a pest.