On privacy: I'm wondering where the researchers got their data. If these were state-owned cell phone providers, then this was very wrong. If private companies... then either the companies violated privacy agreements by giving out the data without consent, or their customers signed away their privacy rights in their service agreement.
On the study itself: Was a study really necessary for this? Yes, people work near where they live, and they do business in this general area... and generally don't go on exotic vacations every day. I'm amazed. Good job, researchers. Maybe for you next (probably taxpayer-funded) study, you can look at how getting shot increases one's risk of death.