Hi,
I've got a 3gs and it works beautifully with Blue and Me for contacts download and making calls - both outgoing and incoming. The iPhone itself doesn't support sending text message details out over bluetooth, so the message reading doesn't work with the 3GS at the moment... who knows, it may one day be added to the iPhone firmware.
The download of contacts was smooth and done in a single go including those contacts who I have several numbers for, like mobiles, landlines, work etc..
When making calls, you just tap the windows button on the wheel and say "Call <name" if there are multiple numbers under the contact you can choose which, and the lady voice asks "call <name> now" and you just go ahead and say "yes" and it dials the number. If you know the type of number, you can just say "Call <name> mobile" and it will directly call the mobile number under that contact after you confirm.
When an incoming call comes in, by default the ringing tone is extremely loud and nearly made me jump to the wrong side of the road... but you can change external volume control on the stereo system through "Audio" menu I believe. it's tricky getting a balance between good volume for the ring tone and the normal Blue and Me voice activation prompts, however I doubt that this is an iPhone only issue. Known numbers in your contacts list appear in the dash with the name of the calling person which is very handy.
I haven't got the iPhone / iPod blue and me kit yet, but when I do, I will report on my experience
It sounds great as you can listen to your music directly from the iPhone and you can also charge the phone on your journey, something which can't be done using a normal iPhone / iPod cable without the Fiat accessory adaptor. Chris@Souls on this forum was offering these at a good price in another forum topic... not sure if this is still available, I hope it is
if there is stock in the UK that is...