Am I to understand that, although Nokia have many Java and Bluetooth enabled phones, unless they release Bluetooth APIs for that particular phone, or series of phones, it is impossible to write Bluetooth enabled Java apps for it? I'm thinking in particular of the 6310i, which has Java and BT, but no BT JSR82 APIs in the Nokia SDK.
your understanding is correct.
Unless nokia has released bluetooth api for a device , you cannot have j2me application for that device.
I am not very sure about the device 6310i , but the above holds true generally.