If I turn on my cellular data on my iPhone 3GS does it cost money?

If I turn on my cellular data on my iPhone 3GS does it cost money?

If you're not using Wi-Fi, then yes. But depending what kind of plan you have. If you don't have data plan, it won't work at all without Wi-Fi.

It doesn't cost a thing, it will let you send mms messages.
turning on 3g costs money