I just posted my experience on this today. Your phone should just sync automatically and show names (based on your compatibility criteria, it's the same as my Samsung).
Nissan Bluetooth | Phone Details | Nissan USA
Search down to your car/phone level.
I bet it's the iPhone software because names shouldn't sometimes work and then not. My car phone book shows and speaks the entry's full name when reviewing, but I don't know what incoming calls look like yet as I haven't had the car long (I imagine it will show names however). I can test and report back. I know it's not the same phone but the functionality should be the same. [Edit] incoming calls show me the name of the person.
Also, I think if your phone has automatic download built in, you can't create individual entries but I could be wrong.