Below is a list of the manufacturers that have, so far, indicated that they will be introducing iOS in the Car to select models of their cars beginning in 2014. The service will be built in to the in-car system, and as of now it seems there are no plans for the service to be added into aftermarket systems.
Again, it will be available in certain car models built by these manufacturers, in new 2014 model cars and beyond. As of now, there's no indication that there will be any way to install the service in an older generation car.
Acura
Audi
BMW
Chevrolet
Chrysler
Ferrari
Ford
General Motors
Honda
Hyundai
Infiniti
Jaguar
Kia
Land Rover
Mercedes-Benz
Nissan
Opel (Vauxhall)
Toyota
Volvo