Meant to write this saturday, but Siri does in fact work with the explorer's bluetooth. So anyone with a new iPhone 4S (or soon jailbroken iPhone 4) will be able to use Siri to read and send text messages, read and write email, schedule appointments and reminders, etc etc.
While the phone is connected to MFT, just hold down the home button to summon Siri, and she will talk through the car speakers, and listen to the car mic.