Is there an app for Android that keeps track of how many MB (or Bytes) have been transfered (sent or received, network usage) through Wifi and/or data connection?
Of course, there are quite a lot actually. Here are just a few examples:
https://play.google.com/store/apps/details?id=com.radioopt.widget&hl=en
https://play.google.com/store/apps/details?id=com.netqin.mobileguard&hl=en
https://play.google.com/store/apps/details?id=com.onavo.android.onavoid&hl=en
I don't think you need an app. I think you just go to settings and check storage space (measured in GB or KB)
