This deal is from the Coles catalogue starting Wednesday 18 December.
IMHO there are 2 great options for using this starter pack. Either way, before you activate make sure you get a promo code from a friend already with Belong for an additional $20 credit.
Option 1 - start out on the $10/month plan. The first 6 months cost is already covered ($40 starter pack credit plus $20 referral credit). This is a good option for those with modest data requirements (average 1GB/month).
Option 2 - start out on the $40/month plan. When the first billing day comes you'll already have 80GB data (minus what you already used). Then switch to the $10/month plan. The first 3 months cost is already covered, and you'll have nearly 80GB banked which never expires and can be used or gifted.
Update for Option 2: If you are activating before 31 December there is this alternative to using a promo code from a friend: https://www.ozbargain.com.au/node/501982
If you are porting your number to Belong then this gives you $50 credit, which you could use to stay on the $40 plan for an additional month and get an additional 40GB (total 120GB), or you could use it for several more free months on the $10 plan.
For more details on plans & billing see the wiki page in Whirlpool. Also there are plenty of discussions in previous Belong deals.
BTW this starter pack may still be available at Woolworths for the same price.
I have a question what if i port my number over on the 29th or 30th of December what would be my billing cycle