Some cars providing this feature when you buy a car but if you dont have it in your car then there is a socket available for that. You have to stick it on to your dash board. It is available for various models. You can search it on your nearest car accessories store.
I recently purchased a iottie car mount on a daily steal site for like 5 bucks and couldn't be happier. It's versatile you can mount on a dash or window if you want. Minde has been suctioned to my windshield since days one and hasn't moved an inch great product.
A lot of it has to do with your specific vehicle and where the iDevice mount is placed.
I have one of those iPhone/iPod mounts that plugs into a cigarette lighter plug. It works, but just barely clears the center console. Also, due to the placement of the cigarette lighter, it more or less renders the front passenger's cup holder inaccessible. In addition, my car has manual transmission, so sometimes my view of my iPhone is obscured by my right hand if it is on the stick shift.
The mounts that sit in a CD slot aren't always better. Some units might actually still be accessible. Others may not. My after-market head unit has a remote which can control most functions of the unit. That's good because a CD-mounted smartphone/tablet holder would obstruct most of the buttons.
You should look very closely at your car's head unit, as well as cigarette lighter plug and determine for yourself if a given third-party mounting solution will work for you. These vary wildly between various vehicles and model years, there's no way to make a specific recommendation.