Have a look at this:
http://www.nissanusa.com/bluetooth/find.html" onclick="window.open(this.href);return false;
It looks like its saying that you can transfer the address book with the 3GS but not with the 4?
Seems like it's the Random Spec Generator (cousin to the Guess-O-Meter).
However, the phone has to have the right stuff. On my phone, a previous rev of the software had all kinds of bluetooth probems, and couldn't upload the phonebook at all. The current rev, however, works fine, including phonebook upload.
EDIT: Page 7-8 (that's section 7, page 8, not 7 thru 8) of the Navigation manual has the info on how to transfer the phone book.