When i got my new HTC Hero i was told i had a 500MB G3 download limit, now every one knows 500MN isn’t much so i’m slightly worried about going over it then been charged loads.
Anyway i have found a free Android app called 3G WatchDog. Its a great and easy to understand app, showing you a data received and transmitted, daily weekly and monthly.
You can also set your monthly download limit and it will warn you when your approaching your limit, and it displays a green amber and red symbol in the top left corner.
You can download 3G Watchdog from the android market