Finally, got around to giving this a serious try. Successfully upgraded the OS to v4.2.1.96. I have a laptop with built-in BT. Laptop and 8700 are successfully paired. Two BT services are discovered: Audio Gateway and Dialup Networking. However, the BT options "Turn on Bluetooth support" and "Configure Bluetooth..." are still grayed-out in the BlackBerry Device Manager. Can it be enabled?

You need to use the Windows drivers for your Bluetooth card in your laptop. If you're using another set of drivers you'll need to uninstall them and just use the basic windows drivers. This doesn't work with all bluetooth cards so it just may not be possible.