Everything you have seen here is on the money. If you download a ton of data, you will eventually get charged. That said.... I have used the bluetooth tethering on the international data plan all over the world. I only tend to use it when I can not get a WiFi connection for my laptop.
As an example, I needed to find a hotel in London and use the company on-line travel site to find an approved hotel. That application won't run on the Bold. I used the tethered Bold to the laptop, ran the app, found and booked a hotel ... all from the rental car as we were negotiating London traffic. (I was the passenger.
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I've used it for similar needs all over the world. But I don't go running bit torrents or download ISO files. I use the tethering for apps that use nominal data that won't raise any red flags over the amount of data being used. It definitely works. And I have not seen any additional data charges as long as I am on an AT&T roaming partner.