I received $15 off every month on Sim only Plans thanks to Vaya.
It should work if you are already on the Vodafone Network and are not in a contract.
1.) Ring Vodafone on 1555 or 1300 650 410.
2.) Ask them to try to match the Vaya $18 sim only plan. http://www.vaya.net.au/?option=Mobile&4Gsimonly&plan=Power Plans
3.) They should offer some sort of discount but I know for a fact that you can get $15 recurring credit for 6 months.
My Plan is the $35 which I only pay $20:
1GB of Data
$500 included value
Infinite Calls to Vodafone
Worked for me and 3 other friends.
Good Luck
Why would I want to be on Vodafail rather than Optus network with Vaya?