Belong NBN owned by Telstra.
Unlimited 100/40 $57/month over 13 months (12 Month Contract) plan.
Follow this procedure:
Belongs billing cycle is from the 2nd of every month. If your connection goes active after the 2nd, Belong does not pro rata the remaining days of that month instead they just give you the rest of the month for free. So signup on the first day of the month or a few days at the end of the previous month to time the activation to begin right on the 2nd to give you the whole of your activation month for free.
When signing up, ask for the Unlimited 12/1 $65 month plan. This will give you one month free(not including the free activation month). You will also get a free speed boost up to 100/40 for the first three months (four months including the activation month).
After the 2nd day of the month after the free activation month (so within the first free month of the 12 month contract) call Belong or login to your Belong account online and downgrade to the 100GB $50/month plan. You will get to keep your existing Unlimited data allowance until the next billing period begins (2nd of the next month).
After the 2nd of the next month and your credit card has been billed $50 for the 100GB plan, login to your Belong account again and upgrade your plan to the Unlimited $65 (It's 12/1 but you are still getting your free 100/40 speed boost). The changes will take effect immediately or within the next 48 hours but you won't get any charge any extra for the data upgrade. The new charges always apply from the 2nd of the next month.
After the 2nd of the next month when your credit card has been billed $65 downgrade your plan to the 100GB $50/Month plan. This change will not affect your unlimited data allowance until the 2nd of the next month.
After the 2nd of the next month when your credit card has been billed $50 upgrade to the unlimited 100/40 $95 month plan. The changes will take effect within the next 48 hours but you won't get charged any extra for the data upgrade until the next billing cycle.
After the 2nd of the next month when your credit card has been billed $95 downgrade to the 100GB 12/1 $50 month plan. The changes won't take effect until the 2nd of the following month.
After the 2nd of the next month when your credit card has been billed $50 upgrade to the unlimited 100/40 $95 month plan. The changes will take effect within the next 48 hours but you won't get charged any extra for the until the next billing cycle.
Rinse and repeat until you reach the end of your 12 month contract. So it should look like this, counting from month 0 (activation month):
0 Free
1 Free (downgrade your plan)
2 $50 (upgrade your plan)
3 $65 (downgrade your plan)
4 $50 (upgrade your plan)
5 $95 (downgrade your plan)
6 $50 (upgrade your plan)
7 $95 (downgrade your plan)
8 $50 (upgrade your plan)
9 $95 (downgrade your plan)
10 $50 (upgrade your plan)
11 $95 (downgrade your plan)
12 $50
13 months total = $745.
So it works out as Unlimited 100/40 $57/month give or take a few days.
In addition, there's also a $20 credit for new signups using my referral code: IAFCXNTG1
This probably won't work. I recently lowered my plan using their online service, it's worked as suggested but I'm still billed for the full amount due to billing issues. There are a few people having similar problems but there's no way to report it unless you sit in on hold for an hour.
Rather than the first month free, i actually paid for a month i didn't even get a service as it took so long to setup. I even got charged by Telstra for all the minutes i went over on my plan sitting on hold with belong. So much for my planned bargain.