There's Amaysim and Internode to name just two - there are others. Most if not all of the non Telstra suppliers use the Optus mobile phone network behind the facade of their own branding.
Amaysim are very good, and well priced by comparison with a couple of others I've checked out. I've been using them for some time with no complaints at all. Unused data entitlement seems to roll over into the next months, and coverage has been ok wherever I've needed it. I'm only using 3G at this stage.
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