My dealer stated the new cradle was "for the iPhone 4", but I didn't think to try to confirm whether that meant designed to accept and utilize the 4, or only compatible with the 4.
Not that it's the same, but you can still connect another device with the USB (and audio) jacks in the armrest storage and the bluetooth will work for the second phone if you're both in the car at the same time. No power, but can receive calls. I'm thinking you want it for when she's driving so she can put it in the cradle for charge, antenna, etc.
Perhaps you're left only the option to apply the whole new-car-justifies-new-phone "logic" . . . .