I've had a nightmare with my Dell i8600 with TM350 and my previous TM300 (upgraded hoping the newer Dell drivers would help). Using either Vista or Dell's drivers give me a dropped connection as soon as the phone begins to sync and I'm under the impression it's because of the Toshiba stack used on the TM300/350 cards. I had it working perfectly for about 2 days and then it just suddenly stopped.... Now I'm back to USB... :(

For references:
Windows Vista Ultimate
Desktop Manager 4.2 SP1
TM350 A00 Dell Drivers & Vista WHQL Driver

The two BlueTooth services, the Bypass and Desktop Manager ones, prompt me for a driver for each of them and nothing works to get them going.