The data sense application "usage" page that shows detailed data usage of each app, shows a "system" icon at the bottom (out of the higher to lower usage order) that currently shows 86 megabytes of usage (20 over cellular network and 66 over wi-fi). Does anyone knows what is this about? What does the WP8 system uses this data for?.... I want to know in order to completely understand my data usage since I am not in an unlimited plan.