I have the W810i and can say that it works with my 330i.
Pairing was no problem.
The address book shows up in the car.
Now for a problem. When making a call, it mutes the stereo, but the call is placed from the handset, not the car.
Now, when you receive a call, it will be placed over the car's speakers. But, you have to tell your phone you want it that way. Here's what you do:
Menu | Settings | Connectivity | Bluetooth | Handsfree | Incoming Call | Check In Handsfree
The above is for a W810i that has no branding. It might be a little different if you have a branded phone.
I was a little concerned that they didn't have an Outgoing Call setting. So, I called Sony Ericsson and asked them about it. Basically, I was told to contact my BMW Dealer.
Well, we all know what they are going to say.
Anyway, that's the lowdown on the W810i.
If anyone has any suggestions regarding outgoing calls, pass them along.