I just discovered that the Ford Sync in my 2013 doesn't support any USB Broadband Modems. This makes this Sync feature useless, and I can't setup my Ford as a 'HotSpot' inside the vehicle. The only way is to 'Tether' your phone, and pay ATT an additional monthly fee.
Support what you sell - USB Broadband Modem support. It's in the documentation, and Sync software.