What are some hidden reasons an employer might provide “free” smartphones for employees?

So they can contact you any time day or night.

Tracking features.

I would NEVER carry or use a mobile that didn't belong to me and only me. 

They actually listen to everything you say.  People think the new iphones only have this "new" annoying feature.
This is not true.  They all do and have since the beginning.
It is a HUGE problem.  
Examples:
You and your doctor talking in the doctor's office.
You and you lawyer discussing topics.
You and your lover pillow talking.
You and your family talking.
You and your financial advisor/banker talking.
You on the toilet after eating chilli.

All of these are about you and your life.  It is NOT open for discussion with anybody not involved in that specific moment or conversation.
Even if you talk to yourself.

... They ARE listening.