Well, if you plan on buying a BMW or a Mercedes, you'll be happy since they both now offer full iPhone integration where you can control the iPhone's music and calling features and view them on the car's navigation/infotainment screen. As for aftermarket radios, I heard that some Alpine and Pioneer radios will work with the iPhone, but only to access music on the phone. It will not control phone functions.

For calling integration, most Bluetooth phone integration kits will work with the iPhone just like any other Bluetooth enabled phone. There are a few iPhone specific kits that include a mount for the phone and either tape deck or bluetooth connection. Some also include a speaker phone and remote mic mounting.

Unfortunately, I have not yet seen a good aftermarket radio, like Alpine or Pioneer, that has true iPhone integration like what's in the new BMWs or Mercedes.

You can get some reasonable adapters that have from just audio support to full control of the iPod. Some will do control of the iPhone as well, and I'll bet you will see more of them in the future. I tossed a couple of links below from places that have the iPod interface to most all stereo with good integration and control for many OEM units. One like my be something that helps, but it really depends on your current stereo. The product from Solisto looks very interesting as well.

Yes, in fact many aftermarket manufacturers are starting to release new products that work with the iPhone. Alpine has a nice double-din unit that is available now.

Some Iphones when plugged like and Ipod will act like a regular Ipod and it should work flawlessly. More and more Stereo manufacturers are making these features built in with both bluetooth and plug in options also.