At $7.50 per 30 days for the first 6 renewals, this is one of the cheapest per-month plans available with unlimited calls+SMS+MMS, and has 2GB of data with data rollover, data sharing and data gifting. Perhaps useful if you're just about to come off a yearly plan, don't need much data, and need an inexpensive plan until another good yearly deal pops up.
After 6 renewals, the price reverts to $10 per 30 days, which is still one of the cheapest prices compared to other MVNOs.
The data rollover is "up to 100GB". Data sharing and data gifting is only to other users on Australia Post Mobile, and has limitations like "Gifting is unavailable if you have under 1.5GB and expires at the end of the recipient’s expiry period".
Australia Post Mobile uses the Optus 4G Plus network, like most other MVNOs do (Coles, Amaysim etc).
It's not yet known if these SIMs are available in Australia Post franchises, so it may be online-only. I went through the checkout process and it told me delivery is free.
Edit: Found in-store, behind the counter, but may not be at all Australia Post franchises. Photo: https://files.ozbargain.com.au/upload/58622/99405/img_202211…
Interestingly, this plan illustrates that some of the price comparison websites are not telling the truth. On Finder, if you sort by price, this plan doesn't show at all unless you manually limit the search to "Australia Post Mobile" plans: https://www.finder.com.au/compare-mobile-plans-under-20
Edit: it now appears on their list, towards the end of providers charging $10, even though it's shown as $7.50. Some other providers appear in the list in the order of their discounted price, but not Australia post. It appears there's preference given to some providers and not to others.
On WhistleOut, this plan doesn't appear at all: https://www.whistleout.com.au/MobilePhones/Search?calls=-1&s…
If you're currently paying $12 per 28 days for Amaysim's cheapest plan, this plan has the same inclusions, lasts longer, and is cheaper - even after the introductory offer.