I'm also driving an '07 GS 350 and using the "Sky Dock" from XM to get both satellite radio and iTunes.
Pros - I have XM / Sirius, iTunes and the Bluetooth phone works / sync's just fine.
Cons - I have a wire hidden / running to my trunk and a magnet antenna.
You shouldn't need to buy an XM account to get iTunes to work so you could buy a new or used Sky Dock and be in business.
Good luck!