Hey guys, guessing this is already known but thought I'd say it again.
Ran out my 1gb this month with a bit of excess phone-age so I called up Telstra to get some more. Paid 10 bucks for an extra 1gb (standard data pack price) to bring my limit up to 2gb. When they upped the limit however they also reset the counter, so I got an extra 2gb in effect for the price of 1 :)
Also note I was able to organize that the operator would automatically cancel the extra data after the next billing cycle. Don't think they can make the computer do it by itself so will be on the lookout to make sure she does it, but yeah it seems it's possible.
Hoping this is news to somebody :)