But 100Mbps is like unnecessary.  Many servers are on 100Mbps (and in the US), so you won't really get that speed anyway.  Difference between, say, 30Mbps and 100Mbps in this day and age really isn't that much IMO.  5GB/mo quota is a joke - need to go on the 200GB/mo plan to actually get any use out of it.
It's probably $88 now, IDK, might try digging out the pamphlet if I do decided to try the special.
That's $78/mo for internet + phone, so better than yours, but still a fair bit more than, say, Exetel's $50/mo for 200GB 24Mbps ADSL2+ and phone.

But yeah, it's only $18, and I wouldn't mind going with it for a few months, but the contract length stuffs that up.  So really, it's actually $18/mo plus opportunity cost of anything cheaper in the future.  As this is Telstra's line, and I don't think other ISPs can simply install their own "DSLAM", it's unlikely Telstra will reduce the costs.  The possible change comes from NBNCo possibly buying over the fibre setup in the next two years, in which case wee'll probably get better deals.
If NBNCo doesn't buy it any time relatively soon, then 2 year contracts probably aren't that bad, but then 24*$18 = $432 for 50% less quota over 2 years isn't exactly appealing either...