Unhappy [Q] Nexus 7 Handsfree calling

Hi All
Here is the thing. I have iPhone (sorry sorry sorry), but it is given by my company so I have no choice. I cannot tether with Nexus 7 because AT&T will not allow due to unlimited data plan. I am planning to use Nexus 7 as the head unit for my car. How do I connect to iPhone? Can I use a handsfree kit that will BT to my Nexus as well as the iPhone and use the tablet to make and receive calls?
How can I get a aux input port with this setup and use Belkin handsfree to plug to the aux in port?
Please please help.