I just recently went though this with my daughter, who get that phone from her mother.
I assume you're using XP?
We made the mistake of inserting the Bluetooth adapter and just expecting XP to "do the right thing", as it usually does.
After several days of loading/unloading/re-installing/searching I found that there is a significant difference between Microsoft's Bluetooth software and what came with the Bluetooth adapter we bought. Also, once you allow Microsoft to associate their driver with the adapter it will remember that association and continue to use it no matter how many times you un-install the adapter and try to install other software.
Once we physically deleted the appropriate file(s) from the system we were able to re-install the driver software that came with the adapter, and then everything worked great. I don't recall exactly how it appeared, but it was fairly intuitive once it worked.
Sorry I can't recall the files to delete (it was several weeks ago). You can probably find them with an appropriate Google search.
John Meissen snipped-for-privacy@aracnet.com