Is Internet modem cost money for iPhone 3G?

Hello everyone. I'm going on a road trip and forgot my card Internet. I get to share the Internet connection to my iPhone 3G so I can connect to the Internet though. So can someone help me? Someone can tell me If it cost money to buy the Modem Internet?

you need to add attachment to your plan of $ 20 and more importantly, if you currently have unlimited data plan you plan to spend limited. Personally, I would not do it, WiFi is almost everywhere.

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