I bought my Nokia 6230 in Hong Kong in February 2005 and used it while doing fieldwork in West Africa. At that time, my firmware was I believe 4.x (don't quote me on that though!). I discovered that there was a Bluetooth bug in that phone's firmware so transferring files over x amount of MB would hang the phone. When I returned to HK in November 2005, I went to one of the Nokia CareCentres and told them about the problem. The took my phone to upgrade the firmware for free and within an hour got it back. In HK, the Nokia policy is that if there is something wrong with the firmware, they'll upgrade your phone for free. So, you could try that tactic. Say that your old firmware has been having problems with the Bluetooth connection. If it's an old firmware, it's likely it has that problem.
According to PhoneDirector, this is what my phone's firmware currently is:
Phone model: Nokia 6230
Phone software revision: V 05.50
Phone model code: RH-12
Network: Cingular, U.S.A.
Network code: 310 17
Connection status: 6