I m not sure about an AT&T 4G modem or another company.....but I do know the Sync3 NAV does not use SD cards. I wonder how a map update will be accomplished.
I do use the FordPass to view the limited data from the Ford Oasis system.
Maybe someone will buy one of the 2017 Ford Service DVD's and let us know what there is in the circuit.
My 2011 has the hard-drive based Sync system (Sync 1?), it does map updates from DVD's.