I have the MB Multi Handset Interface with the latest Bluetooth "puck". Pairs fine, voice quality decent.
One nice bonus is how fast the contact directory loads now. With a V600 directly in the cradle(no BT) it could take up to five minutes to load about 30 contacts. With the iPhone usings BT it loads four times as many contacts in just seconds.
As far as reconnecting when getting back in the car, mine always reconnects and at least loads the recents, but not always the directory, unless the iPhone is fully on.
Has anyone found a good way to check voicemail within this setup? I haven't fugured out how to connect to vmail via the MB controls. Or, if I connect using the iPhone directly, I cannot get the audio to play through the MB.
Also, have you noticed what happens when you try the old speed dial function through the MB keypad?