Vodafone NL, 10 EUR a month capped plan (aka Unlimited)... phone plugged into the computer now posting to you
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It's the "push" setting that will get you when roaming. Of course practically all phones have "push" disabled when roaming by default, or ought to. "push" means that data is sent to your phone either at intervals or as it arrives ie. an email. If you have this turned on while roaming then your phone will happily suck down all this data, often unbeknownst to the user, incurring international roaming charges.
$15 AUD for a MB is highway robbery.