I know for a fact that there are issues. Not only with the Treo 650 but also the new PPC-6601. I hope the are working on a fix that that as well.
A week or so ago some Acura owners complained that their newly-purchased Treo 650s weren't working with their cars' Bluetooth Handsfree links. While that was unfortunately, this whole Bluetooth car thing isn't exactly a science yet, so a little slack was given. Now Blueserker is reporting that it's not just a problem with Acura—many different makes and models of cars, from Toyotas to Chryslers, are having problems getting the link to work correctly (or at all). Posters on the PriusChat forums say that Sprint has acknowledged the issue and is working on a fix (presumably in tandem with PalmOne), but beyond the as-yet-unfulfilled promises from Sprint pre-launch to fix the Dial Up Networking portion of the Treo's Bluetooth stack, no official word has been made.
Bad News for Treo 650 Owners