Well I just read this (take it for what it's worth):
I have a 2010 Ford F150 Supercab with Nav and Sync. Got my iphone 4 yesterday in the mail. I synced it to my truck via Bluetooth and had the same trouble I have seen posted on the web. Everything worked but the phonebook was not uploading so I could not voice dial by name. My iphone 3GS had worked just fine. I found the trouble that has fixed the problem for me entirely. It is on the iphone itself.
Go to Settings, General, Bluetooth, and look under Devices for Sync. Touch the small circled arrow on the right end of the Sync box and you go to a screen that has some settings. Mine had Sync Contacts ON, Phone Favorites ON, and Phone Recents ON. But under that is a setting for "Other Groups" and there are two choices, "None or All Contacts". On my iphone the None box was checked and that was the trouble. I checked the All Contacts box and exited to the Home Screen. Then I started up my truck and let it Sync to the iPhone 4. The Phone book uploaded completely. Problem solved. I have been in and out of my truck maybe 10 plus times today and every time I start it the iphone syncs and uploads the phonebook and I can voice dial by name through Sync.
Yeah that apparently might fix the contacts not downloading to the SYNC system.
My contacts download fine, I just can't hear anything when making outbound or inbound calls.