I don't think there is an easy way to sync an entire phonebook to the iphone nav. This is a limitation of the iphone, not the nav because I was successful with sending my entire phone book to my nav unit with a sony-ericsson phone. The iphone only allows me to send one contact at a time.
Now this was was back in 07' and maybe the new iphone or new firmware enables this feature.
btw- I have an 06 nav unit