Yay! it works!
My Microsoft Surface Pro 2 can use the N900 3G connection.

Currently I have to do everything manually (I guess everything would work the same for Windows 8.1 computers):

1) check that the N900 is "connected" to the Surface (the N900 shows a blue bluetooth icon; if not, open the Surface Bluetooth Settings and connect to the N900; you may need to switch bluetooth off and on, in the same Bluetooth Devices window)

2) on the Surface: open the "Bluetooth Personal Area Network Devices" window in the Control Panel / Networks / Devices (I actually made it a desktop shortcut) and wait a few seconds for the N900 icon to appear

3) select the ugly N900 icon in that window

4) click on the "Connect to..." tab and then on "Connect to access point" (I don't know if this is the exact name in the English release of Windows 8.1) to start using the N900 as a network device.

5) on the N900: start 9000's script at the beginning of this thread.


The current (latest updates) Windows 8.1 version only records outgoing network packets (another Microsoft™ Genuine™ Bug™): in its Bluetooth Network Connection Status dialog, while surfing the web I see lots of packets sent but "0 packets received" (an "ifconfig bnep0" on the N900 shows the actual number of rx/tx packets).

Some notes:

- if the Surface goes in stand-by mode, to connect again when resuming I need to repeat steps 2 to 5

- if I switch to Flight Mode the N900, or reboot/poweroff it, I need to repeat all steps 1 to 5