[vegemite]

Telstra are a complete rip off. No one uses them unless they are forced to. If you need data outside of the cities then Telstra is a better option for coverage, although don't overlook Optus and ISPs that re-sell their data networks over the Optus 3G network. Optus 3G or Vodafone 3G coverage may be sufficient depending on how 'remote' you intend to go.

If you just need voice outside of the cities, forget Telstra, just get a Three SIM, and switch off data when you leave the cities and just use voice for the same price. Roaming on Telstra from Three outside of the cities is 50c / MB so you can still check email or weather or whatever if you need to.

If you don't travel outside of the cities, forget Telstra, go Three or Vodafone.

For super cheap voice, look at companies like Pennytel who give free access to their VoIP voice gateway using a re-sold Optus SIM, and can provide an ok data pack on that although Optus is notoriously over-subscribed so the least reliable for data speeds.

I use Three as I rarely leave the cities and just switch off data when I do except for occasional use, and get 2GB / month in the cities, and it's fine for me.

Yes, Whirlpool is your forum of choice for all things data and voice in Australia.