On an iPhone 4, does just having your 3G on waste Internet?

I always turn the 3G on my phone off at night (I don't have Wi-Fi at my house) because I heard that 3G runs and wastes Internet when it's turned on, even if you're not using it and no apps are currently running on it.

As long as you aren't running any apps, it won't use your data.

You don't have to do that. I have an iPhone 4 as well, and when I got my phone taken away, it wasn't hooked up to the Wi-Fi and the bill for my Internet didn't go up. You only use your 3G if you're using something that needs Internet like safari, twitter, YouTube, etc.
~ I hope I helped