FYI - I use the Kensington Liquid Aux for iPhone and iPod. It uses a single cable to the iPhone/iPod dock connector to both power the phone and route audio through the car's Aux Input jack. The plug for the 12 volt accessory port in the center console is low profile, so it fits perfectly with the console closed. It's like it was made specifically for the IS. There is of course no integration with the NAV system, but it has a remote control with play/pause/skip control and I don't even find a need to use this. It's about $80 and a great solution considering the constraints of the console and the cost of the full blown Lexus solution.
I've also read on the Lexus solution that it's designed for storing the iPhone/iPod in the glove compartment, which I find inconvenient to access and plug stuff into as the driver. It would also negate any satellite radio option you had installed.
One drawback - using the Aux Input jack for the audio system while also powering the iPhone/iPod from the car results in a ground loop and ignition noise (whine). There is a service bulletin on this and I just had it done for my car. Works perfectly now.
http://us.kensington.com/html/14492.html
