While this may backfire, I would say installing tracking software on the phone, then doing many subtle things which gives this away, would be an awesome learning experience.

"Creepy?! What? Google, Facebook, etc do it. What's wrong?"

I feel like hacking the phones of parliamentarians, then setting up a website showing their daily activities, would be excellent.

Double effective if it just keeps happening, even when you say you'll stop, no matter how often they reset or reconfigure the phone.

"What?! Everyone else does it!"