Samsung A411
I found the best solution to be the Samsung A411 on pre-paid if you do not want to switch over to Telstra. This phone(or the A412) is a blue tick and keeps working when most others can't get a signal.
The operating system is a nightmare but the phone works well.
Do a search on whirlpool.net.au for A411 or A412 for more info.
Telstra don't seem to offer the 411 phone any more but you could get one on ebay brand new for $109 buy it now.