I'll add a further point. Voltage does not have the names and addresses. The Judge said that privacy would be protected, but not how. No doubt he will elaborate on that when he actually issues his rulings. It could well be that Voltage have to produce the letter for approval, but it gets sent by an escrow service. We'll know in a couple of weeks.
"I'm quite sure there will not be any 'accidental' letters. Australia is not the US".
Why do you think they would be so stupid as to go down a path which their Australian lawyers will advise them will ensure that they will then lose this case and lead to other sanctions from the Federal Court of Australia?
Very few courts have taken the matter of geo-location very seriously. One that did was a French County Court against the defendant Yahoo! Inc.  In that case the Court heard evidence that estimated the certainty of being able to identify a browser location. Perhaps 70% of users could realistically be located with a reasonable degree of accuracy.
One example of a common glaring error was those users who used the American AOL as a service provider, where the geo-location software pinpointed them as physically being in Virginia, USA.
1. League Against Racism and Antisemitism (LICRA), French Union of Jewish Students, v Yahoo! Inc. (USA), Yahoo France, Tribunal de Grande Instance de Paris (The County Court of Paris), Interim Court Order, 20 November, 2000