here's a though for the OP - the phone only gets data as much as you tell it. nothing happens in the back ground that you aren't aware of or didn't initiate... so if you had it to fetch your data every 15.. there's your hit.. you ever hit the youtube icon? there's more data..

also before you call Apple make sure you know whats going on... you'll get no help from them..

I have push data set to manual, and I have wi-fi at home and work, I called apple they told me their counters are accurate. I spent another hour on the phone to telstra who have said they are having problems measuring the iphone data with their counters

another thing to watch is that its not actually using data unless that little rotating wheel is going. i had a read through the iphone manual, as it's amazing the little features you don't know about that there are.

In order, the iphone will connect to (drops to next if unavailable)

Wifi Last connected to
Wifi in area that you have connected to before
Wifi in area that are available (and it'll ask you to join)
3G

So in my case, i'm at work, so I fit into #2 at the moment. If i try use it when I go on my lunhc break, i'll fall into Cat #3 or 4, depending on what is available.

I'd turn push off, and set it to manually check unless you're at home or work and connected. I'm at work so it's on push and 15min. when i leave this arvo i'll turn it off again till i get home, although I am building a database of all wifi available between work and home!!!

Well thats obvios I see your location is Tasmania. Is that one of those small countries in the Southern Ocean?

Just Jokes!!

You haven't used all that data. If you are like me, this is what has happened.

You bought your phone on the 11th? And got the data pack applied the same day. Your account probably bills on the 20th or something like that (ring Telstra to check but I'll bet it's something like this as the same thing happened to me). So you've been given pro-rata of the 80mb for the period up til your bill date, and then it will reset and you'll get your full 80mb.

What on earth would the iPhone be downloading in the background all the time? Especially seeing that it doesn't support background processes.

The only thing I could think of is auto-fetch, which can be disabled, and which is disabled by default IIRC. However, checking for email every 10 minutes couldn't possibly rack up 64 megabytes of usage in just 5 days. Back of the envelope calc says this would amount to over 80kB per IMAP login and header fetch. This is totally out of the ballpark.

Cheers
Steffen.

This is not totally correct: Optus - About Optus - TAS

Incorect. Optus does have 3G coverage in Tassie, as twinturbo has stated.

Congratulations. I think you are the first. Honestly, the people that DON'T read the manual/do a little research astound me, you'd that that for a $800+ device they'd be willing to invest a couple of minutes skimming through the manual.

In addition to online... you can check via your iPhone!

iPhone option of checking usage didn't work for me on the weekend - but they fixed it yesterday or today...
Is in this thread if you want to know where / how
Telstra iPhone 3G data usage trick