This is not the first time T-Mobile has had issues paying employees for work while they were off the clock. http://www.lawyersandsettlements.com/settlements/02742/tmobile.html

A high balance warning team that would manually evaluate out of pattern usage would be ideal in this situation. However even with a team in place or software to analyse usage, roaming usage on another provider or in another country may not be reported back in "realtime". There is often a delay in usage reporting when more than one company are involved.