When you are using a 3G connection on your Android phone, you might be tempted to watch movies and download songs and images because of an high speed connection. But this might increase your bill to a great extend. My Data Manager is a free tool which keeps track of your data usage.
It can be used to set usage alarms to manage your bill. It can track historical consumption to ensure you are buying the ideal plan and maximize how you use your data. Monitor per app data consumption to understand what apps are consuming the most data, and what apps are almost free.
The app is supported on Android 2.2+