APP > Android: Watchdog -track of your mobile data usage

[rcjordan]

monitor your 3G/4G and general data usage on your phone, and warn if you're in danger of exceeding the limit in any one month. You can also view a traffic history of your phone to see when you used most data, and also set alerts if you approach dangerous points (e.g. 75% of your monthly quota etc)

https://play.google.com/store/apps/details?id=net.rgruet.android.g3watchdog