phone is gobbeling up data

I have 6 employees with iphones and all but one use under 2gigs of shared data per month. The employee that is gobbeling up the data,

isn't doing anything really different from the rest of us, yet his phone is using upwards of 10 gigs a month. We have gone to the At&T store but no-one can seem to help. Has anyone else had a similar issue...and what did they do to cure it?

Thanks.