Telstra's choosing a prepaid model for its iPad plans saves you from being tied into a contract, but means you lose any unused data after 30 days. However, it turns out that if you top up your plan during that time, the unused data will roll over.
David Flynn at APC reports that Telstra has confirmed the rollover plan, which uses the same model as its prepaid Next G broadband: leftover credit is calculated in dollars (not megabytes) and its data value worked out according to the rates that apply on the newer plan. In other words, if you've purchased a $60 6GB recharge and used two-thirds of it but then follow it with a $20 1GB recharge, the leftover $20 will get you 1GB, not the 2GB it originally paid for.
We still don't have a complete picture on iPad plans, with Vodafone yet to announce their pricing. Telstra is still looking like a good pick for more intensive users, while Optus' 186-day plan has its merits if you don't want to be constantly thinking about recharge values.