Sorry but optus' network is so far up the shit with inadequate backhaul you'd have a better time if you shot yourself in the foot. I'm with virgin (who are through optarses network) and the coverage is less than inspiring... and that's before you start using data services.
I hate to admit it but *cough* IMO the Tel$tra network is probably the best out of the 4 networks currently (being Telstra, Optus, Vodafone and 3). That's pretty bloody depressing!