Seems to be a fairly contentious service, with people disputing its overall value, however, Smile seem to be running a discount on their 2 year plan knocking between $25-30 off it depending on your status.
In addition, the long running code of LAUNCH20 (marked as expired in this deal - https://www.ozbargain.com.au/node/383956) seems to stack with it to give the following prices:
$108 for a single
$121.20 for a couple
$135.20 for a family (tried with only one child so it might increase with more dependents)
Alternatively you can use the referral links to get the same discount, but given there's only 3 listed, it'll probably look suspicious if they all get a high number of referrals in the next couple of days :)
N.B. I appreciate it's not as good as the previous 2 year for the price of 1 offer, but I tested all those codes and they seem to have expired.
OP does as good a job as Smile themselves on their homepage, in explaining what the hell 'Smile' is.
For those wondering, it's dental insurance.