Why does my iPhone still charge for Internet even when I'm not using Internet?

So, I recently got a pay monthly plan with my new iPhone 4s.

When i'm out and about I'm usually updating my twitter and Facebook account. But, when I'm put my phone down, 3G still says I'm using it and charging me. So do I have to turn it off when i'm finished? Or is there a much easier way?

Did you go into settings to change it.

tap settings, Wi-Fi, and make sure that you see the blue on. If you see the gray off, that means you're using 3g even though it says 4g.

another way to check is look at the top left side of the screen. If you see 4g, then you're using the 3g. If you see the sonar/radar/sound wave icon, then you're using Wi-Fi.

Download 'Data Usage Defender' App - it'll keep you informed about how much data you're using so you can see whether any usage is no minimal as to not worry about!