I purchased the Sony Ericsson T610 from CarToys, and got service from T-Mobile a week after I purchased my LS430. It took about 10 minutes to get the two talking to each other and I haven't looked back since. The only time I ever have any problems is if I leave the phone in the briefcase and then the briefcase is on the floor. Signal strength can go way down but that isn't a problem with the bluetooth.
If there is one 'complaint' that I have it is that when you have a phonebook full of multiple entries ie home, work, cell, etc. and try to transfer that to the car, it seems to only take the first entry. (just home or just cell). I don't know if I'm doing something wrong or if it is just a shortcoming of the system.
Anyway, that combo works just fine....