As expected, Optus has today officially launched its Optus Rewards scheme, which lets you earn two Qantas frequent flyer points for every dollar you spend with the carrier. That's a useful way to top up your points, though it's unlikely to score you a free flight on its own.
To earn the points, you need to register with the Optus Rewards scheme (which involves an annoyingly poor-quality CAPCHA) and link any services you buy through Optus to your frequent flyer account. (One annoyance: validation of the Optus accounts you have can take up to 14 days.)
Points can be earned on landline, mobile (including prepaid) and broadband services, as well as add-ons such as TV Now and Smart Safe. Note that the services have to be purchased directly through Optus itself; mobile services sold through another brand such as Virgin Mobile or Boost aren't eligible (even though Optus itself owns those brands). You also won't earn points on late or dishonour fees, or if you purchase a handset outright.
Individual customers earn two points for every dollar spent (rounded down to the nearest dollar). Business customers will earn at the same rate until the end of the year, after which it will drop to one point per dollar.
If you're not already a member of Qantas' frequent flyer scheme, you can also sign up for free, skipping the $82.50 registration fee that is normally charged to Australian residents. (Given that there's also a current Jetstar promotion offering no-fee registration and that the Optus offer is ongoing, we wouldn't be surprised if that charge gets quietly retired in the near future.)
Earning extra points is helpful, but the reality is that you'll have to be buying a lot of services to actually score a free flight this way. The shortest single flight (such as Sydney-Melbourne) goes for 8000 points, which would mean you'd have to spend over $300 a month to score one over the course of a year. That wouldn't be impossible if you had a home bundle deal for landline and broadband plus a mobile plan, but it's not going to happen with a prepaid phone (if it does, you're clearly on the wrong plan).
Given that, earning points wouldn't be an incentive on its own to change carriers. A better approach is to choose options that meet your needs, and look at those extra points as a useful way of topping up your balance. (The same logic applies to Qantas' partnership with Everyday Rewards.)