Wanna know when your iPhone is using the internet connection and using your bandwidth/data transfer? Well there is a pretty obvious indicator for that in your iPhone.
When you are using your iPhone and any application is using the internet connection (either via edge/gprs or wifi) It shows a small loading circle sort of animated image on the top of the iPhone screen just next to the network strength indicator on the left top.
If it is using the edge based connectivity, then E is also seen with the animated loading circle indicator (as in image below)
In the above image, on top left, you can see the network strength indicator, and next to it is the E which indicated that the current network is EDGE. The animated loading image next to it is indicator of active internet connection and that data is being transferred at the moment.
If you are using wifi, the E is replaced with the wifi sign or strength indicator for the wifi.
This helps you in knowing when your iPhone is using active internet connection and if any of the application is causing you to lose your credit all the time, so that you can know whenever your iPhone is using the internet connection via EDGE/GPRS or wifi.