As far as I know, Telstra still are the only 4G network in Adelaide. It's a bit hard to work out what the 4G coverage is like, seeing as I haven't been with Telstra for some time, but according to some friends of mine, they've been getting 4G in some rural areas of the state's mid north. Optus, well they're supposed to launch 4G sometime this quarter, but I can see that being delayed, yet both Optus and Virgin Mobile have been selling the 4G hardware for some time to Adelaide customers.
Also, I read Vodafail are supposed to be rolling out a new 4G network that's supposed to be faster than Telstra's, but given Vodafone's reputation of late, that will probably be a fizzer.