Unlike iPods, which are supported by most new cars and most aftermarket head units, iPads could only play music via a standard auxiliary-in headphone jack.
That will no longer be the case when Apple launches iOS 4.2, which will allow for direct connectivity to a manufacturer-supplied or aftermarket system. iPads can't be fully charged from car audio systems, unlike iPods, but a trickle charge will at least keep their audio players running while they're plugged in. The only other downside is that the iPad's screen will go black when it's plugged into a car audio system, meaning that the car's head unit will be the only way to change songs or podcasts.
Apple's iOS 4.2 is due out next month and beta users report that audio systems capable of working with iPhones equipped with iOS 4.0 will work with the latest iPad updates.
The video below shows an beta iOs 4.2 working with Ford's Sync system in a Ford F-150.