The funny part is... Your
own phone is safe, because you choose whether to activate the tracking feature. My Verizon phone (before I switched companies) gave me the option. The problem is that just anybody can activate the feature on
their phone, hide it in your car, and achieve the same effect.
Your former coworker's paranoia wasn't completely unfounded, he was just worried about the wrong phone.
But think about how many people are worried that a GPS navigation system in their car can be used to track them? It's a completely different technology, a completely different issue, and I'll bet bottom dollar that the consumer GPS industry is being hurt by this perception.